Adularia from the Glafirinskoye Deposit (Ulenskaya Group, Khakassia)
Abstract Generated abstract
This paper describes alkaline feldspars from the Glafirinskoye skarn deposit of the Ulenskaya group in Khakassia and evaluates their identification as adularia. Based on field observations, crystallographic descriptions, goniometric measurements, and specific gravity determinations, the study characterizes single crystals, Baveno and Manebach twins, fourlings, and eightlings, noting mainly rhombo-prismatic habits with transitional forms toward other adularia types. The occurrence of adularia in cavities of garnet skarns, on altered fractures in intrusive rocks, and in association with calcite, quartz, sulfides, and other hydrothermal minerals is interpreted as evidence for formation during a post-skarn hydrothermal stage. The author further suggests that adularia may be a relatively widespread mineral in the skarn deposits of Khakassia.
Full Text
ADULARIA OF THE GLAFIRINSKOYE DEPOSIT
(Ulenskaya Group, Khakassia)
E. N. Zykov
The article presents information on alkaline feldspars which, by the appearance of their crystals, should be assigned to adularia.
During the study of the skarn deposits of the Ulenskaya group in the summer of 1947, a large and fairly varied body of material was collected that characterizes the mineralogy of these deposits. Field observations and subsequent laboratory processing of the material made it possible to establish the presence of a number of widespread minerals that had been covered only very briefly in the works of previous investigators. Among such minerals should be included, first of all, the adularia found at the Glafirinskoye and Kaltarovskoye skarn deposits.
The processing of the material collected on adularia was carried out with the aim of studying the morphology of the crystals, as well as clarifying the genetic and paragenetic features of this mineral.
Forms of Occurrence of the Mineral
The adularia of the Glafirinskoye deposit, while generally having a crystal habit characteristic of this mineral, nevertheless display a certain diversity in their morphological features.
One of the characteristic forms of occurrence of the mineral at the deposit consists of drusy intergrowths and individual crystals seated on the walls of cavities in garnet skarns, composed essentially of light-brownish anomalously zoned garnet. In some cases the adularia form small, translucent, usually poorly formed crystals; in others, they form white, slightly yellowish, pinkish, or pink, completely opaque crystals distinguished by more perfect crystal faces. Both varieties of adularia usually have the appearance of simple, untwinned crystals. Cavities in the garnet skarns are often entirely filled with adularia. The secondary copper carbonates and iron hydroxides constantly present here cover with a thin crust the walls of cavities and voids in the garnet skarns, as well as the adularia crystals seated on them.
Another form of occurrence of the mineral consists of drusy accumulations of crystals on the walls of open fractures in intrusive rocks. The latter, along the fractures, have undergone alterations of varying intensity, represented by albitization of plagioclases and the development of muscovite, quartz, rutile, and apatite. In the altered zones along these fractures, grains of adularia develop which, on the free surface of the fractures, form crystalline crusts, druses, and individual crystals, accompanied by calcite and sulfides. In this case the adularia have the appearance of somewhat yellowish translucent crystals, very readily forming...
...twins. A large part of the crystallographically studied adularias belongs precisely to formations of this kind.
In addition to the noted forms of occurrence of adularia, granular accumulations of pink and yellowish feldspar, usually associated with quartz, calcite, epidote, actinolite, chlorite, and sulfides, are comparatively widespread at the deposit. It should be noted that among the granular masses of this feldspar, individual crystals of it were found that have a typical adularia habit. The genetic relationships of these minerals will be considered somewhat below.
Crystallographic study of adularias
At the Glafirinskoye deposit, adularias occur both as single crystals and as twins formed according to the twinning laws usual for alkali feldspars; therefore, naturally, in processing the material special attention was devoted to the study of their crystallographic features. For this purpose, goniometric measurements were made of single crystals and twins of adularia.
Despite the considerable number of specimens with adularia collected at the deposit, the number of crystals suitable for measurement was limited; moreover, its twins proved to be the most favorable for measurement.
A detailed study of single crystals of this mineral showed that the latter have a typical adularia habit, characterized by the predominant development of the form $(110)$ in the zone $[001]$, as a result of which its crystals in this zone have a rhombic character. As a result of goniometric measurements on various adularia crystals, the following simple forms were established: $(110)$, $(\overline{1}01)$, $(001)$, $(010)$, $(130)$, and $(\overline{1}11)$, of which the most widespread and habit-determining are $(110)$, $(\overline{1}01)$, and sometimes also $(001)$. The forms $(130)$ and especially $(\overline{1}11)$ occur comparatively rarely on the crystals.
In their habit the adularia crystals of the Glafirinskoye deposit are rather diverse, and on this basis the following groups may be distinguished. First of all, it is necessary to note adularia crystals short-prismatic along the axis $[001]$, whose habit is determined by the predominant development of the form $(110)$ and by the variable ratio of the forms $(\overline{1}01)$ and $(001)$, expressed in the predominance of the face $(\overline{1}01)$ over $(001)$ in some cases (Fig. 1), and in an approximately equal development of them in others (Fig. 3), with a whole series of intermediate forms (Fig. 2). The face $(010)$ is sharply subordinate to the above-mentioned forms, and on some crystals the second pinacoid is absent. This type of crystal, in its most usual form (Figs. 2 and 3), corresponds to the adularia crystals assigned by Kalb [7, 449] to the Zillertal type, or to the adularia prismatic vertical (rhombo-prismatic) type of A. M. Kuzmin [3, 7].
Another group consists of adularia crystals characterized by approximately the same ratio of faces as the crystals of the preceding group, but differing from the latter by a greater or lesser compression along the vertical axis, owing to which such forms acquire a tabular habit (Figs. 4, 5, and 6). The most common and widespread of this group are the crystals shown in Figs. 5 and 6, whose habit is determined by the predominant development of the faces $(110)$ and $(\overline{1}01)$. Such crystals have a form resembling a trigonal rhombohedron, several...
Fig. 1. Adularia crystal.
T—(110); M—(010); P—(001);
X—($\overline{1}01$)
Fig. 2. Adularia crystal.
T—(110); M—(010); P—(001);
X—($\overline{1}01$)
Fig. 3. Adularia crystal.
T—(110); P—(001); X—($\overline{1}01$)
Fig. 4. Adularia crystal.
T—(110); M—(010);
P—(001); X—($\overline{1}01$).
...slightly compressed along the first and third crystallographic axes, which gives them a resemblance to crystals of the Felsöbánya type [7, 449] or to the adularia rhombohedral type [3, 37].
Somewhat different and distinctive is the crystal form shown in Fig. 4 and observed in a single instance. A characteristic feature of this form is the approximately equal development of the faces (010) and (110), which makes it more similar to crystals of the prismatic-hexagonaloid (pegmatite) type [3, 37].
Between the two extreme members of these groups of crystals (Fig. 3 and Fig. 6), a whole series of transitional forms linking them may be outlined (Figs. 2, 1, and 5).
The crystals shown in Figs. 7, 8, and 9 are distinguished by the presence of the more rarely occurring forms (130) and \((\overline{1}11)\), which, being secondary, do not in the least alter the general appearance and character of the crystals. The latter, for this reason, may be assigned to one of the above-mentioned groups.
Fig. 5. Adularia crystal. T—(115); M—(010); P—(001); X—\((\overline{1}01)\).
Fig. 6—Adularia crystal. T—(110); P—(001); X—\((\overline{1}01)\)
Twinned formations of adularia are represented at the deposit in a very diverse manner; among them were observed and studied both twins proper and fourlings and eightlings. The adularia twins proper, as their goniometric study has shown, constitute regular intergrowths corresponding to two laws of feldspar twinning: the Baveno law—the composition planes (021) and \((0\overline{2}1)\) (Fig. 10), and the Manebach law—on the plane (001) (Fig. 11). Manebach twins of this mineral, as intergrowths of only two individuals on (001), are exceptionally rare, in contrast to the very widespread Baveno twins. The Baveno twins of adularia from the Glafirinskoye deposit differ noticeably in their appearance from those cited by some authors for a number of deposits [6, 316; 8, 555]. A distinctive feature of the Baveno twins of the Glafirinskoye deposit is their “heart-shaped” form, caused by the typical adu-
...by a rhombic outline, composed of a twin of individuals shortened along \([100]\). Baveno twins, illustrated, for example, by Niggle, are formed predominantly by individuals elongated along the first crystallographic axis.
Fig. 7. Adularia crystal.
\(T—(110);\ M—(010);\ P—(001);\ X—(\bar{1}01);\ O—(\bar{1}11)\).
Fig. 8. Adularia crystal.
\(T—(110);\ M—(010);\ P—(001);\ X—(\bar{1}01);\ Z—(130)\).
...equally developed individuals, as a result of which the twins have a characteristic square cross-section (Fig. 12).
Further complication of the twins proceeds in the direction of the formation of quadruplets, representing a pair of heart-shaped Baveno
Fig. 9. Adularia crystal.
\(T—(110);\ M—(010);\ P—(001);\ X—(101);\ Z—(130)\)
Fig. 10. Baveno twin of adularia. Plane of intergrowth \((021);\)
\(T—(110);\ M—(010);\ X—(101)\).
twins intergrowing with one another according to the Manebach law (Fig. 13). The general appearance and character of such fourlings is still determined by the habit of the individuals composing it. Finally, the most complex twin formations are eightlings, formed analogously to the fourlings, that is, consisting of four Baveno
Fig. 11. Manebach twin of adularia.
T—(110); M—(010); X—($\bar{1}01$).
Fig. 12. Baveno twin of potassium feldspar after Niggli.
T—(110); M—(010); O—($\bar{1}11$); Z—(130).
twins of heart-shaped form, intergrowing according to the same Manebach law (Fig. 14).
The above-mentioned twins, fourlings, and eightlings of adularia are a characteristic and fairly widespread form of occurrence of the mineral at the deposit.
The crystals were measured on a single-circle reflection goniometer. As already noted, the number of measured crystals was
Fig. 13. Fourling of adularia.
T—(110); M—(010); X—($\bar{1}01$).
Fig. 14. Eightling of adularia.
T—(110); M—(010).
limited, and individual values obtained as a result of measurement at times showed significant deviations from the data given in the corresponding reference books and manuals. This circumstance may be explained by the fact that the crystal faces are often etched, dissolved, and therefore rough, as a result of which the signals from individual faces were blurred, often without a distinct maximum of brightness. This, undoubtedly, must have adversely affected the accuracy of the observed re-
colors. The results of the goniometric measurement of adularia crystals are given in the following tables (Tables 1 and 2).
Table 1
| Names of faces | Fluctuations of angle values from—to | Mean value | Data according to Koksharov | Deviation | Number of measurements |
|---|---|---|---|---|---|
| (110) : (010) | 50°58′—59°43′ | 59°15′ | 59°23′ | −8′ | 11 |
| (130) : (010) | 29°10′—29°26′ | 29°20′ | 29°24′ | −4′ | 3 |
| (110) : (130) | 29°19′—29°28′ | 29°22′ | 30°00′ | −38′ | 3 |
| (110) : (101) | 68°48′—68°50′ | 68°49′ | 69°19′ | −30′ | 2 |
| (001) : (101) | 49°44′—51°14′ | 50°29′ | 50°15′ | +13′ | 2 |
| (110) : (1̄10) | 61°52′ | 61°52′ | 61°13′ | +39′ | 1 |
Table 2
| Type of twin | Names of faces | Fluctuations of angle values from—to | Mean value | Number of measurements |
|---|---|---|---|---|
| Baveno twin of adularia (Fig. 10). | T″ : T′ | 12°03′—11°58′ | 12°00′ | 2 |
| Fourling of adularia (Fig. 13) | T′₁ : T₂″ | 41°01′ | 41°01′ | 2 |
| Fourling of adularia (Fig. 13) | T′₁ : T₁″ | 11°30′—11°34′ | 11°32′ | 2 |
| Fourling of adularia (Fig. 13) | T₂″ : M₂ | 67°45′ | 67°45′ | 1 |
| Fourling of adularia (Fig. 13) | T′₁ : M′₁ | 67°58′ | 67°58′ | 1 |
| Fourling of adularia (Fig. 13) | M₁ : M₂ | 179°43′—179°45′ | 179°44′ | 2 |
| Manebach twin (Fig. 11). | T″ : T | 44°12′ | 44°12′ | 1 |
| Manebach twin (Fig. 11). | M : M′ | 179°48′ | 179°48′ | 1 |
The geometrical constants calculated on the basis of the measurement results given have the following values: $\beta = 116^\circ 15′$, $a : b : c = 0.6619 : 1 : 0.5593$. The geometrical constants of adularia crystals were calculated from the forms (110) and (101), since on the crystals subjected to goniometric study the form (1̄11) was either absent or did not give good readings. Koksharov [2, 129] gives the following values of the geometrical constants for adularia: $\beta = 116^\circ 03′$, $a : b : c = 0.6585 : 1 : 0.5554$.
Among the other properties of this mineral, the specific gravities were studied. The determination of specific gravity was carried out with the aid of a pycnometer with a capacity of 5 milliliters.
The results of the determination are presented in Table 3.
Table 3
| Variety of alkali feldspar | I determination: sample weight in g | I determination: specific gravity | II determination: sample weight in g | II determination: specific gravity |
|---|---|---|---|---|
| Colorless semitransparent adularia from cavities of garnet skarns | 0,6502 | 2,525 | 0,6859 | 2,578 |
| Yellowish opaque feldspar from a feldspar-calcite aggregate | 0,9937 | 2,520 | 1,0422 | 2,545 |
| Pink opaque feldspar from a quartz-calcite-feldspar aggregate | 0,8311 | 2,522 | 0,7932 | 2,535 |
On the Question of the Genesis and Paragenesis of Adularia
The study of the forms and character of occurrence of the alkali feldspar found at the deposit in the form of typical adularia crystals makes it possible to speak of the hydrothermal genesis of this mineral. The filling by adularia of drusy cavities in garnet skarns, the formation of crystalline crusts and druses on the walls of fractures in intrusive rocks that underwent intense alteration caused by the action of hot aqueous solutions (albitization of plagioclase; formation of quartz, muscovite), and the paragenesis of adularia with calcite and chalcopyrite that is characteristic in this case indicate that the formation of adularia was connected with the deposition of material by hydrothermal solutions, which took place after the main stage of skarn formation, i.e., after the deposition of the principal mass of typical skarn minerals (diopside, garnet).
The scheme cited by A. E. Fersman [5, 320], illustrating the change in the habit of feldspar crystals depending on physicochemical conditions, shows that feldspars whose habit is determined by the predominance of the forms (110) and (\(\overline{1}01\)), i.e., adularia, correspond to a probable formation temperature on the order of 350—250°.
At the Kaltarovskoye deposit, where the presence of adularia has also been established, the deposition of the latter was apparently replaced, in later phases of the hydrothermal stage of mineral formation, by the deposition of apophyllite.
As regards the question of the genesis of the pink and yellowish alkali feldspar occurring at the deposit in the form of granular masses, it is necessary, in our opinion, to call attention to the following features in the character of occurrence of this variety of the mineral:
a) its spatial confinement to those parts of the garnet skarn where such minerals as calcite, quartz, epidote, actinolite, chlorite, sulfides, and some others—whose genesis is considered hydrothermal—are exceptionally widespread;
b) the filling of drusy cavities in garnet skarns by a calcite–feldspar aggregate;
c) the occurrence, among granular accumulations of feldspar, of separate crystals of it having a characteristic adularia habit.
These typomorphic features just indicated make it possible, to a certain extent, to relate the formation of such feldspars to the time of deposition of typical products of thermal mineralization (quartz, actinolite, calcite, etc.). For the final resolution of this question and confirmation of the assumption made, additional factual material is necessary.
Adularia in the skarn deposits of Khakassia is significantly widespread. This is evidenced by its finds at the Glafirinskoye and Kaltarovskoye deposits of the Ulenskaya group, as well as by its identification at a number of deposits of the Karyshskaya group ¹) and at the Kiyalykh-Uzen deposit. P. P. Pilipenko [4, 182] notes the presence of adularia at the Alekseevskoye deposit, where this mineral, in the form of typical adularia crystals, together with garnet, epidote, and quartz, is released along fractures at the contact of syenite with garnet skarn. Kh. M. Abdullaev, who studied the skarn deposits of Central Asia, mentions orthoclase developing in skarn cavities [1, 208], the crystals of which, according to the studies of R. S. Myasnikov, have faceting characteristic of adularia.
¹) Oral communication of G. A. Ivankin.
Conclusions
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The study of the morphology of single crystals and twins of alkaline feldspar makes it possible to assign them to adularia.
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There are grounds to suppose that adularia is a fairly widespread formation in the skarn deposits of Khakassia.
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In their appearance, the adularia crystals of the Glafirinskoye deposit may be assigned to the rhombo-prismatic type, while some of their varieties approach crystals of the rhombo-[[unclear: adjective]] type, with an entire series of transitional forms linking them.
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The paragenetic features and the character of the occurrence of alkaline feldspars at the deposit provide grounds for associating their formation with a hydrothermal stage, separated by a deformation hiatus from the time of appearance of typical skarn minerals.
Literature
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Abdullaev Kh. M. — Geology of scheelite-bearing skarns of Central Asia, publ. by the Uzbek Branch of the Academy of Sciences, Tashkent, 1947.
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Kokscharow N. — Materialen zur Mineralogie, Russlands, vol. V, St.-Petersburg, 1866.
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Kuzmin A. M. — Microcline (an attempt at a systematics of alkaline feldspars). Tomsk, 1948.
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Pilipenko P. P. — On the mineralogy of the Alekseevsky mine of Minusinsk Uyezd. In: Collection in honor of the 25th anniversary of the scientific activity of V. I. Vernadsky, 1914.
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Fersman A. E. — Pegmatites, vol. 1, publ. by the Academy of Sciences of the USSR, 1940.
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Dana J. D. — The system of mineralogy, edition VI, 1900.
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Kalb G. — Die Kristalltracht des Kalifeldspate. Central bl. f. Mineral., 1924.
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Niggli P. — Lehrbuch der Mineralogie, II spez. Mineral., Berlin, 1926.