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ART. XVII. On the Clinochlore of Achmatowsk; by N. von KOKSCHAROV.*

THE green mineral of Achmatowsk, remarkable for its dichroism and its perfect cleavage, was for a long while regarded as identical with the chlorite of Werner. Von Kobellt first remarked the difference from that species of both the Achmatowsk chlorite and another of like characters from Schwarzenstein, and gave to them the name ripidolite (from quis, feather and 1005 stone). G. Rose, observing that the name ripidolite was more appropriately descriptive of Werner's mineral than of that of Achmatowsk, reversed the use of the names ripidolite and chlorite, giving the former to the St. Gothard and Rauris mineral and the latter to von Kobell's ripidolite. Recently, a mineral from Westchester, Pa., has been described by W. P. Blake, as Clinochlore, which is not different from the Achmatowsk species.

The crystals of Achmatowsk according to von Kobell are hexagonal. All other mineralogists have adopted this view. At the suggestion of my esteemed instructor, G. Rose, I made in 1851 many measurements of the crystals, and in my paper I also described it as hexagonal.‡

[The author here observes that his former measurements were made with great care with the reflective goniometer; and that although discrepancies with calculation were observed, and the planes were not always simple in their crystallographic signs, the habit of the crystals appeared to be hexagonal, and this view was hesitatingly adopted. He then proceeds, as follows.]

The observations on my labors of G. Rose and M. Kenngott, and especially a letter from J. D. Dana giving a description of the Clinochlore and its analysis by Mr. Craw, led me to suspect that the crystallization of the Achmatowsk chlorite was monoclinic.

As the Achmatowsk mineral has now proved to be monoclinic and its name has been the occasion of some perplexity in the science, I propose to retain the name Clinochlore for the species, including with it also the Schwarzenstein mineral; and I have consequently placed this name at the head of this article.

*Read before the Akademie der Wissenschaften zu St. Petersburg, Sept. 20, 1854, and published in volume xiii. of their Memoirs.

+ Jour. f. pr. Chem., xvi, 470, 1839.

Verhandl. der K. K. Min. Ges. St. Petersb., 1850 and 1851, p. 163, and Pogg. lxxxv, 519.

[The notes in the original giving the remarks of G. Rose, and Kenngott, and an extract from the letter of J. D. Dana, are here omitted.-EDS.]

(m)

1-00 (1) 1 (0)

The clinochlore of Achmatowsk is a very beautiful mineral species. It ac-((n) companies handsome crystallized varieties of garnet, diopside, apatite and other species, in which this locality is so very rich. Many of the crystals are tabular, while others are lengthened in the direction of the vertical axis, and often they are in druses. A large part of the crystals are unfit for measurement by the reflective gouiometer; but there are some small ones which afford good results. The planes observed are as here enumerated.*

4-00 (2)

-4-(

O(P)

3 (8)

2-8 (c)

3-00 (k)

14-00 (t)

∞ (M, x-3 (v)x-00 (h)|

-6 (d) 6 3(w)

-2 (10

Observed Planes.

The most important combinations are as follows:
I-0, -4-∞, 2, 1, 0, -3, 4.0.

II. (fig. 1)-0,3-0, 1-0,4-0, 3, 1, -2, -3, 4-0.
III. (fig. 2)-0, 1, ∞, 4-, ..

IV. (fig. 3)-0, 1-0,4-0, 3, 1, 0, -3, -3, 4-∞, ∞..
,∞, 4, .

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V.-0,

VI.-0,

VII.-0,

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Putting a for half the vertical axis, b for half the clinodiagonal, e for half the orthodiagonal, and C for the inclination of the vertical axis or a on b.

[*The planes are here presented in a table according to the method of J. D. Dana, showing the several zones of planes; the 1st column being the zone parallel to the orthodiagonal; the 2nd, the fundamental zone; the 4th, that parallel to the clinodiagonal. The symbols are essentially Naumann's, except that the letter P is dropped. The letters used by Kokscharov on his figures are also given-Only part of the figures of the memoir are here copied. In figure 2, the lettering is altered, to correspond with the notation, only i is wiritten for o; O, I, 1, 4i, i are respectively P, M, o, t, h, of Kokscharov.-D.]

SECOND SERIES, Vol. XIX, No. 56.-March, 1855.

23

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Also, u for the inclination of the clinodiagonal terminal edge on the axis a; v, for the same on the diagonal b; 9, for the inclination of the orthodiagonal, terminal edge on the axis a; X, for the inclination of a face of P on the clinodiagonal section; Y, ibid on the orthodiagonal section; Z, ibid on basal section.

And also: X', Y', Z', and u', ', for the corresponding angles in the negative hemipyramid :-we then find

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σ

The angle o being 60°, therefore the plane angles of the basal planes are 120° and 60°, or when the acute angle is replaced, a regular hexagon. This hexagonal character is also strongly shown in the planes of the zone m-3, whose intersections with the edges of the basal plane are 150°, and which correspond to the zone m-2 (or intermediate hexagonal pyramids and prisms) of the hexagonal system. The compound crystals consisting of three crystals, which are common in the clinochlore of Achmatowsk, have a still greater similarity to a hexagonal prism.

It is also to be observed that the angle C, 62° 51', is nearly half the angle of M: M, or 125° 37'-half of 125° 37', being 620 481. In the crystals, the hemipyramids of the fundamental series are mostly more or less striated parallel to their intersection with P(0), and seldom smooth and shining so as to afford good measurements. The faces of the clinodiagonal zone m-, are rather smooth and lustrous; but the face P, and the planes of the zone m-3 are the brightest and smoothest. The following angles are obtained by calculation from the values of the axes given, excepting those with an asterisk which are measured angles:

oP 102° 7′ (102° 6'†)

OM 143° 57'

on 163° 34' of 122° 0'

ou (over M) 130° 10'

oo (over i) 121° 28'
oh 119° 16'

nn (over y) 127° 53'
nP 118° 32′ (118° 28't)
ny 153° 57'

nM (over o) 127° 31'
nt 124° 31' (124° 31't)
mP 113° 28'

mi 150° 6' (150° 0'†)

mh 117° 18'

mt 124° 4'

mk 125° 27'

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Obtained from the measured angles; M: M=125° 37'; M: P=113° 57′;

=

P:0 102° 61'.

† Observed angles.

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For the forms, X, Y, Z, etc., have the following values:

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Cleavage very perfect parallel with the base. G. 2.774 according to G. Rose. H.-25. Strongly dichroic, being green in the direction of the vertical axis and brown or hyacinth-red transversely, and the colors seldom so different in other dichroic species. Streak-powder light greenish-white. The largest crystals often only translucent on the edges; the smaller subtransparent. Flexible in thin plates but not elastic.

Although the basal plane is usually smooth and shining, there is in some crystals an unevenness which indicates by its stellate appearance a regular composition. In the crystals of Achmatowsk, this compound structure is quite common; they consist of three simple crystals, compounded parallel to the plane 2. Since the faces of the form are inclined to the clinodiagonal section 60°, and to the basal plane 89° 43', the three crystals will meet at angles of 60°, and have their basal planes inclined to one another 179° 25', or very near 180°.† The large crystals are often also made up of a mixture of small crystals with their basal planes grouped in rosettes, as happens in the specular iron of St. Gothard. * Observed angle.

It might be suspected from such twins which are like those of Aragonite, that the plane P may make an angle of 90° with the base, (as in the mica of Vesuvius); but the appearance of salient and reëntering angles on the cleavage face of these compound crystals seems to be good evidence that the angle between P and the base is not a right angle. In the collections of P. von Kotschubey, there is a large druse of Clinochlore crystals in which each is a twin of three crystals. [In twins from Westchester, there is no reëntering angle, the cleavage plane being perfectly smooth.-D.]

According to G. Rose, the Clinochlore of Achmatowsk has the following characters: B.B. on charcoal intumesces, becoming yellowish brown and opaque: in the platinum forceps, fuses with a strong heat on the outer edges to a black glass. In a tube undergoes the same changes as on charcoal giving little water with no fluoric acid. With borax dissolves easily to a clear glass, colored by iron; with salt of phosphorus a similar glass, the silica separating; with soda on charcoal, a brown swollen mass which fuses with difficulty. With sulphuric acid wholly decomposed. Analyses by von Kobell (J. f. pr. Ch. xvi, 470), Varrentrapp, (G. Rose, Reise n. d. Ural, 1842, ii, 127 and Pogg., xlviii, 189) and Marignac (Ann. de Ch., x, 430).

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This composition does not differ from that of the Clinochlore of Pennsylvania.

I shall have to revise my comparisons of the described chlorites, after this reference of the Achmatowsk mineral to the monoclinic system, with the exception of the Schwarzenstein chlorite (ripidolite of v. Kobell), as they cannot stand, since we do not know to which zone the described planes of these chlorites belong. I may here observe that none of the angles obtained by Frobel and Descloizeaux in Pennine, are yet found in either of the zones of the Achmatowsk chlorite. The same is true of the Kämmererite. The resemblance of the clinochlore crystals to hexagonal forms, renders it desirable that there should be a revision of the crystallography of all these minerals.

The optical characters of our crystals have not yet been fully studied. I can only state that the laminæ of the Achmatowsk clinochlore examined with the tourmaline, allows the light to pass when the axis of the tourmaline plates are at right anglesin which respect it does not differ from biaxial crystals. There is a strong probability therefore, that the optical characters are like those of the Pennsylvania Clinochlore. In this last, Mr. W. P. Blake, examining a triangular plate, found that the two axes lie in the same plane which was at right angles with one side of the triangle; and this plane therefore lies in a clinodiagonal section. According to Blake, one of the optical axes is inclined at an angle of 27° 40', and the other at 58° 13', making the angle between them 85° 53' and 94° 7'.

Mr. Blake has observed in another specimen a second system of axes, the plane of which makes an angle of 60° with the first, which indicates that the specimen was a compound crystal.

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