Prof. A. M. Kuzmin

ON HEXAGONAL GOLD

I.

In the autumn of 1935, former graduate student M. A. Zheromsky delivered to me several very small gold crystals, which had been discovered by engineer V. I. Gordeev during his investigation of one of the sludge settling basins of the Berikul plant, from which cyanide solutions were drawn by means of a siphon for their subsequent distribution among the zinc precipitators.

When examined under the microscope, the gold crystals found appeared unusual to V. I. Gordeev and M. A. Zheromsky, and rather resembled crystals of a hexagonal type. This crystalline form, unusual for gold, prompted V. I. Gordeev to transfer the material he had obtained to me for the appropriate investigation.

Publication of the information reported below, and of the conclusions following from the study of these gold crystals, was delayed somewhat owing to the expectation of additional material, the receipt of which was delayed by unforeseen circumstances.^1

II.

The material received through M. A. Zheromsky consisted of a small number of gold crystals, the dimensions of which, as may be judged from measurements, do not exceed: in length 0.22 mm, in cross-section—0.060 mm (Table 1).

Table 1

Individual measurements of crystal size

^1 The material of this article was presented on March 27, 1937, at a meeting of the Tomsk Branch of the Mendeleev Chemical Society.

Gold crystallites were represented both as single crystals and as intergrowths of them having the character of twins. Of the crystal forms on the crystals, the faces chiefly developed are those of the hexagonal prism \((10\bar{1}0)\) and of the pinacoid \((000\bar{1})\). In addition, there are imperfectly developed faces, which are represented by faces of a hexagonal bipyramid, probably close to \((10\bar{1}1)\).

Fig. 1. Gold crystals

When individual gold crystals are examined, the following may be noted.

1. A separate gold crystal, on which the faces of the prism and pinacoid are developed; the edge between the faces of the prism and the pinacoid is truncated by a face of the bipyramid, somewhat matte and giving no reflection (Fig. 1).

2. Two gold intergrowths represent two crystals that have grown together in parallel by the faces of the prism. In one intergrowth the gold crystals bear only the faces of the prism and pinacoid. In the other intergrowth, on the crystals, besides the usual faces of the prism and pinacoid, narrow faces of the bipyramid develop, lying in the same zone as the prism and pinacoid (Fig. 2).

Fig. 2. Parallel intergrowth of two gold crystals

1. The next gold crystal is an intergrowth of a relatively large crystal of clearly hexagonal appearance, bearing, as a rule, faces of the prism and pinacoid, the edge between which is truncated by a narrow strip of a face of bipyramidal form. A small prismatic gold crystallite is attached to the just-described crystal, parallel to the plane of the pyramid (Fig. 3).

Fig. 3. Gold crystal with an accreted second crystallite of smaller size

1. On another specimen we have a gold intergrowth of three crystals, where to the prismatic crystal, relatively larger in size, another crystal, somewhat smaller in magnitude, is attached at a right angle; to this latter, likewise in a direction perpendicular to the principal crystallographic axis, is attached a small crystallite also of clearly hexagonal-prismatic character (Fig. 4).

At the boundary of intergrowth of two crystals that are relatively large in size, there develops, at first glance, a spongy mass of gold, which obscures part of the seam between the intergrowing crystals and part of the prism faces located near this seam. On greater magnification the spongy mass proved to be composed of complex submicroscopic gold crystallites, likewise of hexagonal form. On relatively large crystals, narrow strips of bismuthide are developed.

Fig. 4. Twinned intergrowth of gold crystals

Fig. 5. Twin of gold

1. In one of the intergrowths we also have two equally developed crystals of clearly prismatic character. Both crystals intergrow along a plane parallel to the normal bismuthide face (Fig. 5).

2. Finally, one specimen represents a complex formation of gold, consisting of several crystals of approximately the same size, and several small prismatic gold crystallites grow onto one of them perpendicular to the edges of the prism; the area of the prism faces between the bases of the small crystallites has a somewhat spongy character (Fig. 6).

Fig. 6. Complex group of gold crystals

Fig. 7. Gold crystal, twisted about the vertical axis

1. Cases of deformation of gold crystals during growth are—

...are expressed in a certain curvature of them along the axis, and hatching appears on the faces parallel to the edge of the prism and the pinacoid.

1. On one crystal of gold, bearing only the faces of a prism and a pinacoid, a certain twisting about the vertical axis of the crystal is noticeable (Fig. 7).

Thus, for all the gold crystals sent by V. I. Gordeev, their prismatic character and the combination of prism and pinacoid, accompanied by narrow faces of a bipyramid, are characteristic. Taken all together, this sharply distinguishes these crystals from crystals of the cubic system.

III.

The color of hexagonal gold is reddish, with a somewhat yellowish tint. This coloration stands out especially sharply if the crystallites of hexagonal gold happen to be adjacent to gold of the ordinary golden-yellow color.

IV.

The question of the occurrence and obtaining of gold crystals of hexagonal character has been raised repeatedly in the literature. However, for lack of convincing materials, crystals of gold are still regarded exclusively as belonging to the cubic system, to which they were first assigned by Haüy and Rome de l’Isle (1, 296)^1. The investigations by G. Rose of crystals of native gold, as regards their belonging to the regular system (3,4; 30, 198), confirmed the conclusions of Haüy and Rome de l’Isle (3, 4). Later, in major survey works and works of reference character, P. Groth (5, 6), C. Hintze (1, 236), E. S. Dana (7, 14, 15; 38, 16), V. I. Vernadsky (2, 269; 7, 263), N. Leitmeier (9, 187), A. K. Boldyrev (10, 86, 96), P. Niggli (11, 131) and H. Schneiderhöhn (37, 63), and in individual works, e.g. G. Rath (12), Helmhacker (13), P. M. Eremeev (14), and others, consider gold as cubic, while the deviation of its crystals from regular forms is interpreted as a distortion due to elongation or shortening of the crystals as a result of their growth along the trigonal axis of symmetry. Such an interpretation, without a critical approach—at times very categorical (16, 292)—may not have been especially useful for an impartial examination of certain contradictions that already existed at that time with regard to the crystalline forms of gold.

Apparently, the first information on hexagonal gold belongs to Zenger, who in 1861, on the basis of microscopic measurements, recognized the gold crystals he studied as hexagonal, and regarded the cuboid forms as rhombohedra with an angle between faces of 88° 4′48″ (1,239, footnote). However, in

^1 The figures in parentheses set in bold type indicate the serial number of the bibliographic source; those set in ordinary type indicate the pages of references.

In 1862 Kenngoth, as C. Hintze says, was able to refute Zenger’s assertions and to show the incorrectness of his arguments (1, 239, footnote). Unfortunately, C. Hintze did not consider it necessary to examine critically the arguments and objections of the investigators just mentioned.

In 1878 A. H. Chester, while working on gold, observed on its imperfect crystals forms of a hexagonal prism (5, 6) and faces of a pyramid (15, 313), whose polar angle was equal to 46°.

Later, in 1885, W. P. Blake, on octahedral crystals of gold from Elancro in Montana, found very small prismatic crystals of gold, inaccessible to measurement, which possessed a hexagonal character and terminated in acute pyramidal forms. The same author also described small crystals of gold from Sonora in California, which bore faces of a hexagonal prism, faces of a pyramid, and a basopinacoid. The dihedral angle \(\infty P : P = 50^\circ\). Incidentally, these crystals were regarded as analogous to the gold crystals of A. H. Chester (15, 313). E. S. Dana considers this similarity improbable, since A. H. Chester’s crystals were obtained from gold amalgam by treating it with nitric acid, as were the crystals from Sonora, which were likewise obtained artificially (15, 313).

In 1893 information on gold with a hexagonal aspect appears in several articles (16, 17, 18, 19).

A. Liversidge, over a number of years engaged in studying gold in quartz and calcite veins and its formation in placers and the metallurgy of gold, comes to the conclusion that in the crystallized state it is encountered extremely rarely (16, 291). According to his data, in primary deposits gold is usually found in the form of irregular scales, grains, and hair-like and wire-like formations. In more or less clearly crystallized forms, according to his observations, gold can be encountered only in relatively soft rocks—calcite, clays, serpentines, and others. A. Liversidge supposed that, being in solution in meteoric waters, it is deposited around nuggets of gold, which owe their origin to primary deposits. The crystallized gold observed by this investigator, in its forms, closely corresponded to hexagonal prisms and occurred in the form of plates and stars; and he did not encounter it in clearly recognizable crystals of the regular system (16, 291).

Experimental investigations of the precipitation of gold from solutions enabled A. Liversidge to obtain it in the precipitate in the form of hexagonal prisms, plates, and stars, which, among other things, were deposited on grains of gold placed in the solution. Observations of the natural forms of gold crystals and of the forms obtained by precipitation from gold solutions made it possible for the investigator to assert that gold can crystallize in forms of the hexagonal system (16, 291).

Miers, referring to A. Liversidge’s data and in no way entering into a critique of the possibility or impossibility of the existence of hexagonal forms of gold, categorically objects to this investigator’s conclusions and says that every form of gold may appear as regular, but each of them may develop along an axis of symmetry of the third order and thereby deviate from regular forms (16,292). Further, he believes that the hexagonal plates and prisms of gold are merely crystals of the cubic system shortened or elongated along the ternary axis (16,292). P. Groth agreed with this objection by Miers to A. Liversidge, considering that the hexagonal forms of gold can be interpreted only as regular ones developed along the trigonal axis (5, 6).

As was noted above, in the same year, 1893, articles by F. V. Wil’m and E. S. Fedorov were published on the hexagonal aspect of gold crystals. F. V. Wil’m, repeatedly treating gold amalgam with nitric acid, obtained reddish and yellow-brownish globules which, when pressed with a glass rod, easily disintegrated into a granular powder. The same picture was obtained if gold was dissolved in sodium amalgam and then treated with nitric acid. The gold crystals obtained in this latter case were relatively larger in size and were represented by shining needles and prisms up to 2–3 mm long, grouping together, growing through one another, into star-shaped formations. The prismatic forms of the gold crystals terminate in oblique faces (17;18, 326).

F. V. Wil’m believes that the small gold crystals he obtained from the amalgam contain mercury, which forms a solid solution with gold (17,258). This is probably not entirely so. One should think that the gold crystals form on the amalgam before it has time to decompose under the action of nitric acid, and for this reason the mercury is captured by the gold crystals during their further growth. Similar cases of the capture of mercury by gold also occurred in the experiments of A. N. Chester when he obtained gold in crystals.

The small gold crystals obtained by F. V. Wil’m were studied by E. S. Fedorov. At the latter’s disposal were prismatic small crystals with shining faces; the thickness of the crystals did not exceed 0.025 mm. They were studied on a universal goniometer. Measurements of the prism zone gave angles close to 60° (19,456, 457). The terminal faces of the crystals do not lie in one zone with the prism faces and occupy a position corresponding to that of the faces of a rhombic dodecahedron (19, 457). However, the author qualifies this by saying that the terminal faces, being insufficient in size and giving unsatisfactory reflections, did not permit their exact crystallographic significance to be established (19,457).

Despite the incompleteness of the data obtained in the study of crystals of hexagonal aspect, E. S. Fedorov believes that

they can in no way be regarded as a polymorphic variety of gold, for the crystals of F. V. Vil’m belong to the cubic system and prove merely to be elongated along an axis of the third order (19,458). However, E. S. Fedorov, in his conclusions on the character of F. V. Vil’m’s crystals, relies on the corresponding conclusions in connection with the study of analogous forms described by G. Rose (3) and G. Rath (11).

As early as 1887 E. S. Dana described crystals of gold from Oregon, where it occurs in the form of delicate dendrite-like formations composed of clearly formed crystals bearing an acute rhombohedral aspect. Here, too, individual crystals were encountered which have the appearance of hexagonal pyramids—forms which on other crystals receive only subordinate and very weak development (20, fig. 3; 6, 15, fig. 7, 8). The faces of the hexagonal pyramid are truncated by three tetragons. According to E. S. Dana, the position of the planes on the gold crystals under consideration and some¹ measurements provide grounds for revealing their cubic character (20, 276). The impression produced of rhombohedral symmetry is explained by the author as a proportional distortion of the crystals in the direction of the threefold axis (20, 276). Therefore all the faces present on the crystal in this case are regarded as faces of the icositetrahedron (311). However, the faces present on the crystals, as E. S. Dana notes, may with equal success also be regarded as faces of acute (4041) and obtuse (2025) rhombohedra and of a hexagonal bipyramid (2243) (20, 277).

E. S. Dana, in the case of distortion just noted, sees one of the examples of pseudosymmetry and the tendency of a series of crystals of one symmetry to imitate crystals of another, while preserving rational symbols of the faces (20, 277).

However, in considering E. S. Dana’s images of the gold crystals, one may agree, with some strain, that the tetragonal faces, which look like faces of obtuse and acute rhombohedra, are faces of the icositetrahedron; but in that case we must recognize the trigonal faces of the same crystals as icositetrahedral, produced as a result of non-isometric growth of the crystals. Further, the few measurements mentioned by E. S. Dana can hardly be regarded as sufficient to confirm the deviation of the given type of crystals from the ideal form with preservation, in the case described, of a series of dihedral angles. On this basis we are entitled to join the opinion of A. K. Boldyrev, who says that the gold crystals from Oregon in appearance resemble trigonal combinations rather than cubic ones (9, 96).

A. Lacroix, describing gold deposits situated in the territory of French possessions, notes that in cavities of quartz—

In living veins of the Andavakaera deposit on the island of Madagascar there occur gold crystals elongated along the threefold axis with faces \((311)\), which in their character prove to be identical with E. S. Dana’s gold crystals from Oregon \((21, 845,\ \text{figs. }1\ \text{and }2, 846)\). Gold crystals of a similar character, according to A. Lacroix, are also found in other deposits of the same island \((21, 846)\).

In 1903 N. Averkiev published an article on the precipitation of crystalline gold from solutions by means of formaldehyde. He indicates that gold can be reduced from solutions by oxalic and sulfuric acids, ferrous sulfate, and formaldehyde. Using the last reagent for precipitation, the author obtained relatively large gold crystals, visible to the naked eye. Verification of the experiment showed that gold in crystalline form is obtained only from strongly acidified solutions \((17, 329, 330)\). In this case plate-like crystals up to \(0.8\) mm across are obtained. The crystals have trigonal and hexagonal outlines, and in the latter case three, probably prismatic, faces bounding the gold plate are larger in size, while the other three such faces lying between them are noticeably smaller \((22, 334,\ \text{figs. }3\ \text{and }5)\). The author himself, in the observed thin plate-like crystals, wishes to see combinations of the cube and octahedron and the forms \((110)\), \((hkl)\), \((hkk)\) \((22, 334)\).

In the present case we can only state that gold crystals prefer to develop perpendicular to the threefold axis of symmetry, and we regret that the investigator in his article gives no indications specifying his considerations concerning the forms just enumerated.

In 1912 E. Hatschek and A. L. Simon, working to clarify the formation of gold in quartz-vein deposits, experimented and observed the precipitation of gold from solutions in a siliceous gel. The gold was precipitated by various precipitants, both liquid and gaseous, and the formation of crystals of this metal proceeded sometimes relatively rapidly, sometimes very slowly. In a number of experiments the authors obtained lustrous plates and leaflets of gold of hexagonal and triangular outline \((23, 266)\), closely resembling the plate-like crystals of N. Averkiev, i.e. the hexagonal plates resembled, as it were, a combination of two trigonal prisms. The crystal plates obtained by the authors were very thin and showed through with a greenish color.

If N. Averkiev’s plate-like crystals grew on the bottom of his crystallizers, then in E. Hatschek and A. L. Simon’s case they were obtained suspended in the hardening gel; i.e. in the present case the form of the plate-like crystals obtained cannot be so simply explained by distortion due to the impossibility of uniform growth of crystals growing on the bottom of crystallizers.

In concluding this brief review of the literature on gold having a hexagonal aspect, it is necessary to note that, alongside cubic gold, gold occurs in hexagonal forms, which predominantly have either a prismatic or a tabular habit. Crystals of prismatic character bear the faces $(10\overline{1}0)$, $(0001)$, and $(10\overline{1}1)$; among these, the prismatic faces always receive predominant development. As the basal pinacoid develops, in some cases it blunts the apical angle of the bipyramid, while in others it acquires predominant importance over the faces of the bipyramidal form; and on some crystals of V. I. Gordeev only the faces of the prism and the pinacoid are developed. These considerations, as we have seen above, follow from the observations of A. N. Chester and W. P. Blake and from my own. The crystals of F. V. Wilms also bear the faces $(10\overline{1}0)$ and $(01\overline{1}1)$ of the rhombohedron and, in their character, do not in essence contradict the other gold crystals of hexagonal aspect.

The tabular crystals of E. Hatschek and A. L. Simon, as well as those of H. Averkiev, hardly contradict the hexagonal character of the crystals.

One of the remarkable features in all cases of obtaining gold crystals of hexagonal character is an acidified medium.

The unusual gold crystals from Oregon, described by E. S. Dana and also noted by A. Lacroix in Madagascar, bear a clearly expressed ditrigonal character; and their assignment by A. K. Boldyrev to the cubic system seems somewhat doubtful. He is more inclined to regard them basically as a rhombohedral combination (10, 96).

V.

The establishment, for gold, of crystals of the hexagonal system entails the resolution of the question of its polymorphism, against which E. S. Fedorov at one time objected (19, 457).

H. Leitmeier, speaking of gold in the Handbuch der Mineralchemie, indicates that allotropic forms of crystalline gold are not reliably known (9, 187). According to his data, J. Thomsen, on the basis of thermochemical investigations of gold, comes to the conclusion that, alongside its ordinary forms, there exist two more modifications, each of which differs only in thermal properties (9, 187). J. Thomsen, dwelling on the thermochemical features of the modifications obtained by him in precipitates (31, 356, 358, 366), notes only the morphological features of the precipitates, their color and luster; but these modifications of gold were not subjected by him to crystallochemical and crystallographic investigations.

H. Louis, relying on the literature data available from G. Rose (3, 4), J. Thomsen (31), and L. Knaffl¹, accepts for gold at least two allotropic states (24, 329). Modification of gold a has a yellow coloration and the crystalline forms proper to it of the cubic system. The second modification of gold b is amorphous according to H. Louis, and, unlike the first, is red, brown, and purple-red (25, 329). Both modifications of gold precipitate from solutions of sharply different character in concentration and differ in their behavior toward amalgamation (9, 187; 24, 330). The amorphous modification of gold is unstable, and, as H. Louis showed, on heating to 600–700° for no more than one and a half hours the amorphous variety is transformed into the crystalline one without any appreciable thermal effect (25, 85); at the same time it turned out that upon heating within the limits 450–600° or 400–483° gold, passing from the amorphous into the cubic modification, changes its color to yellow (25, 85).

From what has just been set forth it follows that the two modifications of gold of H. Louis—the crystalline and the amorphous—will probably be analogous to Thomsen’s two modifications, obtained by him in precipitates (31, 356, 366).

As was noted above, E. S. Fedorov did not find it possible to recognize, in the hexagonal habit of gold crystals, F. V. Vil’ma’s indication of its polymorphous variety (19, 457).

Further, W. Stein, studying the coloration of metals, especially gold, established the phenomenon of dichroism in thin plates of gold (26, 175). In this connection V. I. Vernadsky says that the phenomenon of dichroism in thin plates of gold even indicates the non-belonging of these plates of gold to the regular system, and it is very probable that “in thin plates gold belongs to another polymorphous variety” (2, 269, footnote). However, in this conclusion one cannot fail to recognize an extremeness which is not justified by any existing data and which requires the assumption that the gold initially formed in plates is hexagonal and subsequently is transformed into cubic.

And finally, P. Groth, who as early as 1906 considered that gold crystallizes only in crystals of the cubic system (5, 6), and supported objections against the opinion on the existence of hexagonal gold (5, 6), in 1921, in his work Elemente der physikalischen und chemischen Krystallographie, speaking of polymorphism, notes that a polymorphous variety of cubic gold is gold possessing clearly expressed uniaxial properties (27, 263).

The discovery by engineer V. I. Gordeev of the above-described crystals of gold in hexagonal forms and similar to the forms of the crystals of A. N. Chester and H. Blake evidently inclines one to the thought of accept—

¹ Dingl. polut. Journ., 1863, vol. CXVIII, p. 282.

to know that alongside cubic gold there exists polymorphic gold, to which a hexagonal structure is characteristic and which, under definite conditions of formation, every time gives stable forms in the shape of hexagonal prisms. To this polymorphic variety must also be assigned those prismatic crystals of hexagonal appearance which A. Liversidge and F. V. Wilm obtained from the corresponding solutions. The gold crystals obtained by N. Averkiev, E. Hatschek, A. L. Simon, and others, with a preferred direction of growth perpendicular to the axis of the third order, are also probably crystals of the hexagonal system. In exactly the same way, crystals of gold of hexagonal appearance are encountered occasionally under natural conditions. Among such formations should be included the gold crystals of E. S. Dana from Oregon and of A. Lacroix from the island of Madagascar, and certain gold crystals from the Southern Urals described by P. V. Eremeev.

The assignment of gold crystals of hexagonal appearance to crystals of the hexagonal system, probably to the ditrigonal class, coincides with the new opinions of P. Groth on the possibility of distinguishing for gold its uniaxial modification, and is supported at the same time by the old data of W. Stein and by V. I. Vernadsky’s considerations on the polymorphism of gold.

A certain uncertainty that exists at the present time consists in the lack of clarity as to whether the crystals of gold should be regarded as belonging only to the holohedral class of the cubic system (11, 131; 5, 6; 6, 323; 14, 37, 38), or whether they should be assigned to one of the hemihedries without axes of the fourth order, as V. I. Vernadsky allows (2, 269; 8, 263), or, finally, following A. K. Boldyrev, whether the crystals of cubic gold should be regarded as belonging now to the hexaoctahedral, now to the hexatetrahedral type of symmetry (10, 86; 28, 115). This duality in the understanding of crystals of cubic gold, while denying polymetamorphism, apparently follows not so much from the imperfection of its crystals as from a number of impossibilities, probably, in studying many of their features which would allow one to arrive at a single opinion on this matter. It seems to me personally that in the dual behavior of cubic gold one could see, in exactly the same way, a manifestation of polymorphism, i.e., crystals of hexaoctahedral and hexatetrahedral (2, 269, footnote; 29, 278) character could be regarded as polymorphic varieties differing from one another in their structural features.

The study of the thermal properties of gold allowed Thomsen to distinguish and differentiate modifications which, perhaps, also correspond to two modifications of cubic gold.

Thus, on the basis of the material presented above, it appears possible to distinguish for gold three crystalline polymorphic modifications: two cubic and one hex-

hexagonal. However, the considerations just set forth merit further and more serious investigations in this direction. The case of the precipitation of crystals of hexagonal habit from solutions oxidized to one degree or another attracts attention and raises the question whether each of the possible modifications of gold may not be characteristic of certain genetic conditions.

VI.

If we turn to the data of X-ray investigations of gold both in the form of formations corresponding to the composition of the element and in the form of alloys with other metals and metalloids that form mixed crystals, it appears that gold—possibly—has a greater number of polymorphic varieties than we can assume on the basis of its crystallographic studies on the material with which we usually come into contact.

Thus, M. Neuburger, in his summary work on the X-ray study of metals and alloys (32), gives, with respect to gold, the following data, compiled by him in a table (32, 200).

Table 2.

Types of lattices of alloys of gold with metals and metalloids

\(^1\) 32, 186. \(^2\) 32, 74. \(^3\) 32, 53.

The first thing that strikes one in this table is the rather great variety of lattice types that is characteristic of the given alloys. This variety will be still more striking if we compare the lattice types of the initial products with the type of lattice of the corresponding alloy. For example, in the alloy AuCu, as is evident, a tetragonal lattice appears (32, 57—65), whereas for the initial products a centered lattice is characteristic; for tin, tetragonal, cubic, and rhombic lattice types are characteristic, whereas for the alloy AuSn a hexagonal one is characteristic. The same lattice character appears in the alloys of Sn with Cu, Ni, and Pt. For Zn we have a hexagonal lattice type; in alloys of gold with Zn, lattices of cubic character appear in various proportions. Only in the alloy Zn₂Mg does a hexagonal lattice type appear, and even that is somewhat different from the lattice characteristic of metallic zinc.

If we take into consideration Grimm’s law concerning the formation by metals of mixed crystals in alloys, possible only under chemical and physical homotypy, i.e., two metals can give a mixed crystal only if their space lattices are similar (33, 198; 32, 8) and they produce the same action in crystals (34, 82), and if we also take into account the very important conclusion of V. M. Goldschmidt that isomorphism, and consequently also the formation of mixed crystals, is rather a consequence of the structure of the compound, of the molecule, than of its chemical composition and the chemical affinity of the two or several bodies forming the compound (34, 73), then from the table just presented it follows that for gold in its various compounds no fewer than 7 types of space lattices are possible, for each of which there will be its own typical elementary parallelepiped.

If we look at analogous data for Cu and copper alloys with other elements, it will turn out that copper must have no fewer than 11 types of space lattices. For Sb and its alloys no fewer than 9 lattices have been established, for As—no fewer than 7, for Al—no fewer than 9 lattices of different types (32, 200—207, table 107).

From this we may draw the bold, yet not unfounded, conclusion that, probably, every element, including gold, may possess a large number of lattice types, each of which is stable only under special conditions; this is what is revealed in alloys and, probably, will also be revealed in salt compounds.

Confirmation of the conclusion just set forth, concerning the possible multiplicity of polymorphism for elements, may be found in A. E. Fersman’s Geochemistry. A. E. Fersman, developing O. Hahn’s proposition concerning the ability of substances present in solution in a finely dispersed state to give mixed crystals with substances precipitating from the same solutions in cases where this finely dispersed substance enters into the space lat—

lattice of the substance crystallizing with it (36), indicates that the ions of elements are captured from dilute solutions by another lattice only if, in their dimensions and in their type, they can form with it an isomorphous structure, and if this structure is energetically more favorable than the pure crystal (35, 371). In other words, this finely dispersed substance—that is, the tenant, entering the lattice of, say, the “host”—does not disturb its uniformity of crystalline geometry. This means that in the given case the “guest” is capable of possessing a lattice similar to the lattice of the “host,” is capable of adapting itself, of being rearranged in accordance with the circumstances. Accordingly, one may perhaps say, on the basis of the study of the crystalline state of alloys, that the spatial lattice of an alloy, by the character of its structural plan, in accordance with its energetic and physical properties, may deviate from the geometrical structure of the spatial lattices of the original products, as we have seen in fact in studying the structures of a number of alloys. This deviation is still more striking in salt compounds, the geometry of whose spatial lattices at times differs very sharply from the geometry of the lattices of the original products.

VII.

What has just been said confirms once again that, under natural conditions, gold may occur, in comparison with cubic forms, also in other geometrical forms. The possible variety of spatial lattices makes quite realistic the suppositions of V. I. Vernadsky and A. K. Boldyrev that cubic gold may occur not only in forms of the hexoctahedral class, but also in forms of the tetrahedral, pentagonal, and other classes.

VIII.

In conclusion, regarding the finding of hexagonal gold, it should be noted that the occurrence of gold in the tailings of the Verkh-Isetsky plant raises, in turn, a question of practical character: whether new methods can be found for the complete recovery of gold from its cyanide solutions without resorting to zinc precipitants, and thereby cutting the hydrometallurgical process in half.

LITERATURE

1. Hintze, Carl, Dr., Handbuch der Mineralogie. Bd. I, 2. Lief., 1898.
2. Vernadsky, V. I., An Essay in Descriptive Mineralogy, vol. I, 1901, pp. 268—275.
3. Rose, G., Ueber die chemische Zusammensetzung des gediegenen Goldes, besonders des Goldes vom Ural. — Poggen. Annal. d. Phys. u. Chem. 23 Bd., 1831.
4. Rose, G., Ueber die Krystallformen des Goldes und des Silbers. — Poggen. Annal. d. Phys. u. Chem. 23 Bd., 1831.
5. Groth, P., Dr., Chemische Krystallographie. I Tl. 1906.

1. Koksharov, Nikolai, Materialien zur Mineralogie Russlands. Vol. 6, 1870, pp. 321—350.

2. Dana, E. S. Descriptive Mineralogy, 1900.

3. Vernadsky, V. I., History of the Minerals of the Earth’s Crust, vol. I, issue II.

4. Leitmeier, H. Gold — Doelter C. and H. Leitmeier, Handbuch der Mineralchemie. Vol. III, 2nd half, 1926, pp. 186—285.

5. Boldyrev, A. K. Course of Descriptive Mineralogy, issue I, 1926.

6. Niggli, P. Lehrbuch der Mineralogie. II. Second edition, 1926.

7. Rath, G., Mineralogische Mitteilungen. 1. Zur Krystallisation des Goldes — Zeitschrift f. Kryst. u. Miner. Vol. I, pp. 1—8.

8. Helmhacker, R. Gold von Sysertsk am Ural. — Mineral. Mittheilungen. I, 1877, pp. 1—12.

9. Eremeev, P. M., Description of several minerals from gold-bearing placers on the lands of the Orenburg Cossack Host and on Bashkir lands. Mining Journal, 1887, III, pp. 263—309.

10. Dana, E. S. Ref.: Blake, W. P., Prismatisch ausgebildete Goldkrystalle. — Zeitschrift f. Krystall. u. Miner. Vol. X, 1885, p. 313.

11. Miers. Ref.: Liversidge, A., Krystallisation des Goldes in hexagonalen Formen. — Journ. Roy. Soc. South Wales, 1893, 27, — Zeitschrift f. Krystall. u. Miner. 1893, Vol. 25, pp. 291—292.

12. Wilm, F. V., On crystals of gold containing mercury, Journal of the Russian Physico-Chemical Society. Vol. XXV, 1893, pp. 656—667.

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1. Italics mine.—K. ↩