Mineralogical News.-In 1871, Tschermak discovered that the optical characteristics of the various pyroxenes depended in great measure upon the proportion of their iron constituent. He found that with increase of iron there was a corresponding increase in the size of the optical angle, and also in the inclination of the acute bisectrix to the vertical axis of the monoclinic varieties. In later years Wiik, Herwig, and Doelter examined monoclinic pyroxenes with the view of deciding as to whether Tschermak's observations would be found to apply generally. Their results, however, were not conclusive. Very recently G. Flink,' of Stockholm, declares, as the result of investigations made on diopside, schefferite, and rhodonite, that the crystallographic angle ẞ varies with variation in the percentage of iron, increasing with the increase of this constituent and decreasing with its decrease, but within very small limits (22'). The morphotropic action of manganese is to diminish the size of the angle and to carry the crystallization of the pyroxene over to the triclinic system. The value of this angle for different proportions of manganese is given as follows:

Diopside (Mn == free). Schefferite (MnO = 8.32%). Rhodonite (MnO = 41.88% ). 74° 11' 73° 53' 71° 1534' The optical angle and the angle of extinction in the plane of symmetry both increase with the rise in the percentage either of iron or manganese. The geometrical, optical, and chemical properties seem to show that the diopsides among the pyroxenes form a continuous series analogous to the plagioclase series among the feldspars.In the course of the above investigation Flink had occasion to work over a large series of diopside, schefferite, and rhodonite crystals, the results of which he incorporates in his paper. On diopside from Nordmark, Sweden, he finds the following new forms: P, P7, P—2P∞, —†P, and †P. Schefferite is the name given by Mikaelson to a manganeserich diopside from Långban. According to Flink its composi

It crystallizes in red, brown, or black crystals bounded by the planes OP, P, P., 2P, P, P, and-P. The habit of these is determined by the greater or less development of the three planes op, P, and P. Twins are very common according to the ordinary law of the pyroxenes. The axial ratio is: a:b: c=1.1006: 1:0.59264. B=73° 53'. In thin section the mineral is almost colorless. It possesses very weak pleochroism. It extinguishes 44° 25' in the clinopinacoidal section, is positive and 2Va=65° 3' for yellow light. Rhodonite usually occurs massive. But few fine crystals have heretofore been described. In the article under

1 Zeitschrift f. Kryst., xi. p. 449.

∞

discussion Flink mentions the fact that he has become possessed of a large collection of good crystals from Pajsberg and Långban. These he examines, and finds on them nineteen forms new to the species. The axial ratio as calculated from his measurement is: a:b:c=1.0727: 1:0.52104. The inclinations of the axes to each other are a=76° 41′ 52", B=71° 15′ 15", r=81° 39′ 16". The plane of the optical axes is inclined to OP and 'P at 63° and 38% respectively. It corresponds to ,P,16. The acute bisectrix is perpendicular to the plane PTT and is probably negative. 2Va=76° 12' for sodium light and p < absorption b>a>c. The intergrowth of minerals of analogous composition has within the past few years been proven to be very much more common than was formerly supposed. The microscope has revealed the fact that very many rock-forming minerals, as, for instance, the pyroxenes and the feldspars, very frequently occur intergrown with lamella of analogous but slightly different composition. The method of etched figures has shown the same statements to hold good in regard to minerals which occur only in massive form. By the latter means Baumhauer' has succeeded in detecting irregular intergrowth of various substances in cloanthite and smaltite. The occurrence of thin lamellæ of ilmenite in crystals of magnetite from the chlorite-schist of Greiner in the Zillerthal, is placed beyond doubt by the separation and analysis of the two components of these crystals by Cathrein.2

Little bournonite3 crystals cover the cubic faces of galena from Prîbram. Their long axes are either parallel to the combination edge between O and O, or they are inclined to this at an angle of 45°.

Crystallographic News.-The twinning law of lepidolite from Schüttenhofen, in Bohemia, is the same as that for the more common micas,―i.e., the twinning plane is P. The dispersion of the axes is very similar to that in the hemihedral crystals of the orthorhombic system. Intergrowths of muscovite and lepidolite take place parallel to the twinning position of micas of the same composition.- -Several brief communications on the crystallography of topaz have lately appeared. In one H. Bücking5 discusses the forms appearing in the topaz of Mexico, with reference more particularly to the Durango crystals. A large number of new planes have been detected. A second article, by Fr. Feist, describes a crystal of topaz from the Ilmengebirge.

The Zeitschrift für Krystallographie for the past few months has contained quite a number of short articles descriptive of single

Zeits. f. Kryst., xii. p. 18.

3 C. Hintze, ib., xi. p. 606.

5 Ib., pp. 424 and 451.

2 Ib., p. 40.

4 R. Scharizer, ib., xii. p. 1.

Cf. also Des Cloizeaux, Bull. d. I. Soc. franç. de Min., 1886, p. 135.

7 Zeits. f. Kryst., xii. p. 434.

=

crystals of different minerals from various localities. Gehmacher1 gives a series of measurements on the faces of colorless zircon crystals from the Pfitschgrund, in the Tyrol.—————The axial ratio of datholite from the Seisser Alps, as calculated by Riechelmann,2 is a:b:c=0.63584: 1:0.6329. The angle 8-89° 54'-The new forms P, P, 4P7, 13P3, §P, and P (?) have been added to the list of planes occurring on anatase 3 by Seligmann.—The same investigator has measured pyrrhotite from the druses of basalt from the Cyclopean Islands. The results indicate that the mineral crystallizes in the hexagonal system with the axial ratio: II: I: 1.65022.—In the same article Seligmann describes a wolframite crystal from the Sierra Almagrera in Spain, on which are the two new forms -2P and -3P3. The mineral is monoclinic with the axial angle ß=90° 26′ and the axial ratio 0.82144: 1:0.87111.—New crystallographic planes have also been discovered by Sansoni on calcite from Blaton, Belgium. Sansoni 5 also mentions the fact of the tendency in barite crystals from Vernasca, Italy, for the prismatic and end faces to converge towards the free end of the axis to which they are parallel, and along which the crystals have their greatest develop

ment.

Miscellaneous.-The diamonds found in the African diamondfields occur in the immediate neighborhood of volcanic pipes cutting carbonaceous strata of Triassic age, and containing as inclusions pieces of the shales forming the greater part of the series, through which they break. The richest yield of the gem is obtained from the outer portion of the pipes, where the included fragments are most abundant. The rock composing the lower portion of the pipes is quite fresh. It is a peridotite of which certain portions are diamantiferous, while other portions contain no diamonds. The diamantiferous variety is crowded with fragments of shale, while the non-diamantiferous variety is free from them. From these and other facts it is concluded that the diamonds are secondary minerals produced by the reaction of the lava (with heat and pressure) on the carbonaceous shales in contact with and enveloped by them. A study of the occurrence of diamonds in other regions seems to indicate the correctness of this conclusion, as Mr. Diller' points out the fact that in most American localities where diamonds are known to occur the same relation of carbonaceous shales and very basic eruptive rocks has been observed to exist. Mr. O. A. Derby, on the other hand, does not accept this explanation for the origin of the

Zeits. f. Kryst., xii. p. 50. 3 Ib., xi. p. 337

6 H. C. Lewis, Geol. Magazine, 7 Science, Oct 1886, p. 392; Geology of Elliott Co., p. 27. 8 Science, Jan. 1887, p. 57.

2

Ib., p. 436.

4 Ib., p. 352.
5 Ib., p. 355.
January, 1887, p. 22.

also Geol. Survey of Kentucky; Report on the

diamonds of the Brazilian fields.In the lower greensands at Flitwick and Sandy, in Bedfordshire, England, Mr. A. G. Camero1 has found ironstone nodules filled with water, which they lose by evaporation when left exposed to the action of dry air.

'Geol. Magazine, August, 1886, p. 381.