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have been changed into hornstones and knotty schists. Besides the granites the only other intrusives cutting the slates are two dykes of minette, both of which show the effects of pressure. One of the dykes consists essentially of orthoclase and two generations of biotite. It contains also apatite and zircon and large quantities of plagioclaseand calcite. In the squeezed phase of the rock the biotite has been changed to chlorite. The material of the second dyke differs from that of the first one, only in that it has been more thoroughly squeezed and consequently has suffered greater alteration.
Petrographical News.—Sears'finds that the porphyritic feldspar in the rock from Marblehead Neck, Mass., called bv Wadsworth8 trachyte, are anorthoclases, and that much of the feldspar of its groundmass is of the same nature, consequently the rock is a keratophyre. Analyses of the rock and of one of its phenocrysts follow:
Si0, TiO, A1,03 Fe,03 FeO MnO CaO MgO K,0 Na,0 P,Os Ha0 Eock 70.23 .03(?) 15.00 1.99 .24 .33 .38 4.99 4.98 .06 2.19
Felds. 65.66 20.05 tr. tr. .13 .67 .18 6.98 6.56 .41
The report of the State Geological Board of Michigan' contains brief microscopic descriptions of certain eruptive, sedimentary and schistose rocks of the Upper Peninsula by Drs. Patton and Lane. Among the former are described granites, syenites, serpentine and 1amprophyres. Among the sedimeutaries graywackes, quartzites and slates, and, among the foliated rocks, amphibolites and hornblende schists. The amphibolites are principally altered diabases. Quartz diabases are mentioned by Lane as existing in dykes cutting graywackes and slates that are sometimes changed on the contact into spilosites, and quartzites that are altered near the intrusive into Lydian stoue. Dr. Wadsworth, in the same volume, gives an outline scheme of his classification of rocks (eruptive and sedimentary), the principles of which were first ennunciated at length in his Lithological Studies.10
Graeff11 has found, in an old hand specimen of tephrite from Horberig in the Kaiserstuhl, a holocrystalline basic concretion with a structure approaching that of theralite.
'Bull. Mus. Comp. Zool., Vol. XVI, p. 167.
8 Proc. Bost. Soc. Nat, Hist., XXI, p. 288.
9 Rep. State Board of Geol. Survey for 1891-92. Lansing, 1893.
10 Mem. Mus. Comp. Zool., 1884, XI.
11 Versamm. Oberrh. Geol. Ver. Ber., XXVI, 1893.
A modification of the microchemical method for determining iron in minerals is given by Lemberg.11 It consists in producing Turnbull's blue from the ferrous sulphide precipitated on the mineral in question.
Alurgite and Violan from St. Marcel.—Among the minerals from the Manganese mines of St. Marcel, Piedmont, alurgiie and violan haAe always excited considerable interest because of their rich color and their variety. The alurgite was described by Breithaupt as a deep red mica. Penfield" has recently obtained a sufficient quantity of the material for study. He describes it as monoclinic in crystallization and micaceous in habit. Its cleavage plates are flexible and somewhat elastic. It is biaxial with 2 E„ = 56° 32' (average) and its dispersion is ? > v, but often plates show a uniaxial optical figure, due, as the author supposes, to twinning. The mica is one of the first order, and in spite of its dark color, its pleochroism is very slight. Density = 2.835 —2.849. H = 3. Composition:
SiO, A1,0, Fe,03 Mn,0, MnO MgO K,0 Na,0 H,0 Total 53.22 21.19 1.22 .87 .18 6.02 11.20 .34 5.75 = 99.99
In the formula H R, (Al OH) Al Si,0„, R = K and Mg OH. Alurgite is thus a distinct species, which is more nearly allied to lepidolite than to muscovite, although it is a potash mica. The alurgite is associated with a jadeite composed largely of a soda-rich pyroxene that is pleochroic in pale rose and pale blue tints. Its density is 3.257—3.382, and composition (mean of two analyses):
SiO, Al,O, Fe,0, Mn,0, MnO MgO Ca,0 Na3O K'0 Ign Total 54.59 9.74 11.99 1.06 .58 5.03 7.24 9.32 .24 .37=100.16
corresponding to Na R(Si03), in which R = Al, Fe'",Mn'". The mineral occupies about the same position in the pyroxene group as glaucophane does among the amphiboles. In composition it agrees most closely with the chloromelanite from Mexico analysed by Daraour."
For purposes of comparison with this pyroxene, the author analysed a specimen of violan whose density was 3.272 — 3.237, with this result.
SiO, A1,0, Fe,03 Mn'0, MnO MgO CaO Mn,0 K,0 Ign Total 53.94 1.00 .86 .88 .36 16.63 23.80 1.22 .05 .66 = 99.44
The figures indicate a mixture of the diopside, jadeite and acmite mole
"Zeits d. deuts. geol. Ges., 1892, p. 823.
u8. L. Penfield. Amer. Jour. Sci. XLVI, p 288.
1, Bull. Soc. Min. d. Franc, IV, 1881, p. 157. Of. also foot-note No. 30.
cules in the proportions 90.8 :4.1 : 2.4, with the addition of 2.7% of the molecule Na Mn (SiO,),. The mineral is essentially a blue variety of diopside, differing from the anthochroite of Igelstrom16 and from the blue pyroxene of Merrill and Packard.16
Zonal Plagioclase.—Herz" has shown by a study of the position of axial planes in successive zones of zonal plagioclase, and by the values of the respective cleavage angles, that the zonal banding in this mineral is due to the concentric growth of envelopes of different composition. The axial planes and the cleavage angles always correspond with the extinction angles in the corresponding band. It had been suggested by Grosser that the regular decrease in the extinction of the shells of a zonal plagioclase is due to difference in the orientation of the successive envelopes and not to a difference in their chemical composition. Herz's work proves conclusively that the decrease in the value of the extinction is not due to differences in orientation of the same chemical substance.
Hercynite in Gabbro.—Small octahedra and large irregular masses of the green spinel hercynite occur in an altered gabbro at LePrese, in the Valtellina, Switzerland. According to Linck,18 it is found as irregular granular masses within the rock, and as small octahedral crystals enclosed in its plagioclase and associated with corundum sillimanite and biotite. The spinel includes small quantities of biotite, small plates of ilmenite, resembling the plates in hypersthene, a little pyrite, etc. An analysis of tolerably pure material yielded:
SiO, Alfi, Fefi, MgO FeO Total . 1.59 59.62 3.10 9.38 25.30 = 98.99
which corresponds to (Fe Mg) A],0, in which Fe : Mg = 3:2.
Optical Constants of Topaz.—Four Japanese topaz crystals and one crystal of the same mineral from New South Wales are described by Hahn,19 and some of the optical constants of the former have been determined. One of the crystals from Otamjama near
16 American Naturalist, 1890, p. 74. 16Ib., 1892. p. 848.
"Min. u. Petrog. Mitth. XIII, p. 341.
18 Sitzb. d. Kon-preuss. Akad. d. VViss. zu Berlin. Phys.-Math.-Classe., 1893, p. 47. "Zeits. f. Kryst, XXI, p. 334.
Kioto, has the following refractive indices and optical angles for yellow light: ,3 = 1.(5182, r= 1.6252, 2 V = 62° 40', 2 E = 114° 31'. The crystal from New South Wales has 2 E = 113° 18'.
Mineralogical News.—Stover announces the discovery of fine celestites in the Jurassic schists of Brousseval in France. Their axial ratio is .7803 :1 : 1.2826, and index of refraction for sodium light = 1.6235. The crystals are one centimeter in length, and are elongated parallel to ii. Similarly habited crystals occur also in the marl of Ville-sur-Sault. The axial ratio of these is .7806 : 1:1.2797, and density =: 3.991.
Rheineck,0 has made another attempt to calculate from the published analyses general formulas for tourmaline that will not only represent the composition of all varieties of the mineral, but which will also express its relationship with micas. He concludes that there are two alkaline varieties, viz.: Al4 Si, B Hs016 and Al, Si, B, H, 0,„ and two magnesium varieties, Al, Si6 B, Mgt0,6 and Al, Si6 B, Mg, O,,, by whose, intermingling all other varieties are formed.
Several crystallographic observations of Baumhauer11 are of interest. A yellow diopside from the Canton of Graubiinden (Grisons), Switzerland, has an axial ratio a:b:c = 1.0918: 1 : .5879, with /9 = 74° 12' 15". Binnite crystals from Infeld in the Binnenthal are certainly tetartohedrally hemihedral, as the author has succeeded in finding upon them, well-developed, the planes § and 4jp.
Oebbecke" mentions the occurrence of topaz with feldspar, apatite, tourmaline, fluorite, etc, at Epprechtstein and its existence in the granite of the Gregnitzgrund in the Fichtelgebirge.
The arsenopyrite of Weiler in Alsace occurs in an arkose from which Scherer,5 has obtained crystals sufficiently large for measurement and analysis. These crystals are prismatic in habit, and have'an axial ratio a : b: c — .6734 : 1 : 1.1847. A mean of two analyses gave figures corresponding to Fe : S : As — 1: .9933 : .9751.
Mallard" has come into the possession of some beautiful little crystals of periclate that were found implanted on a white compact crust produced in the culcination of some.of the Stassfurt materials.
Several twins of aragonite from the tunnel of Neussargues in Cantal,
» Zeits. f. Kryst., XXII, p. 52.
» lb., XXI, p. 200.
»lb., XXII, p. 273.
M lb , XXII, p. 62.
"Bull. Soc. Franc. Min., XVI, p. 18.
France, are reported by Gonnard58, and some fine crystals of pinite" from Issertaux, near St. Pardoux in the Auvergne.
Miscellaneous.—In his development of the theory of the constitution of the micas, Clarke,' has reached the problem of the lithium members of the group. This he solves by supposing lepidolite to be an admixture of the simple molecules Al F, Si, 08 R,', in which R' is principally lithium, and Al, (Si04), R,', in which R3' may be either K,H or KH..
Retgers,8 suggests molten phosphorus and a solution of phosphorus in CS, as media for use in determining the indices of refraction in highly refracting substances. A tiny fragment of the phosphorus may be melted between two object-glasses, when it spreads as a thin sheet between them, and, upon cooling, remains transparent. Its refractive index is 2.144. That of a saturated solution of the substance in CS, is 1.95.
Some time ago, Damour,9 suggested the name chloromelanite for one .of the varieties of jade found in ancient implements. He discovers now that the material contains garnets and pyroxene. It thus resembles the rock eclogite. The pyroxene from a Mexican specimen is composed as follows:
Si0' A1,0, Fe3O, CaO MgO Na3O Total Sp. Gr. 56.57 17.21 8.86 4.44 2.12 10.70 = 99.90 3.37
Nordenskjold30 has begun the study of snow crystals. The first contribution to his discussion is a series of handsome photographs of a large variety of flakes, including prismatic, stellar and other forms some of which contained liquid enclosures at the time of their fall.
a lb., XVI, p. 10. MIb , XVI, p. 16.
"Bull. Am. Chem. Soc., XV, May, 1893.
18 Neues Jahrb. f. Min., etc., 1893, II, p. 130.
"Bull. Soc. Franc. Min., XVI, p. 57. Cf. also foot-note No. 14.
*IIb., XVI, p. 59.
Reprinted from The American Naturalist, May 1st, 1894-.