276 DESCRIPTIONS OF MINERALS, 
morphic rocks. Found in the lava of Vesuvius; in the 
Tyrol ; Faroe Islands, Iceland ; in imbedded crystals in some 
doler yte of the Connecticut Valley. 
At Hanover, N. H., anorthite crystals occur altered to a silicate 
which afforded, in an analysis by Hawes, only 2°2 of lime, and, in place 
of the rest of this ingredient, 7°11 of potash, 3-77 of soda, 1:10 of iron- 
sesquioxide, and 2°67 of water, with 3005 of alumina and 52°52 of 
silica ; which compound, if the water be made basic, has the ratio 
nearly of labradorite, though distinct from that species in the alkalies, 
and also in specific gravity, which is 2°96 or very nearly 3. It has some 
relation to zoisite, and to typical saussurite, but is widely different 
in constituents and ratio; it is related also to jadeite. (See page 
263.) 
Labradorite.—Lime-soda Feldspar. Labrador Feldspar. 
Triclinic. Angle between the cleavage planes 93° 20' and 
86° 40’. Usually in cleavable massive forms. 
Color dark gray, brown, or greenish brown ; also white or 
colorless. Often’ a series of bright chatoyant colors from in- 
ternal reflections, especially blue and green, with more or 
less of yellow, red, and pearl-gray. 
Composition. #CatNa,Al O,, 8i,;= Silica 52°9, alumina30°3, 
lime 12°3, soda 4°5—100. Sometimes contains a little potash 
in place of the soda. B.B. fuses quite easily to a colorless 
glass. Only partially decomposed by hydrochloric acid. 
Obs. A constituent of the larger part of eruptive rocks, as 
doleryte, and amphigenyte, and many lavas ; and also of some 
metamorphic rocks. Occurs as an ingredient in part of the 
Archean rocks in North America, and was named from its 
first discovery in Labrador. 
Andesite. Triclinic. Angle between the cleavage planes 87°-88°. 
Near labradorite in scott pester The formula $CaiNa, AlO,, Si,= 
Silica 59°8, alumina 25 5, lime 7:0, soda 7°7=100-0. 
Hyalophane. Monoclinic, and hence angle between the cleavage 
planes 90°. A baryta feldspar ; the formula like that of andesite, ex- 
cepting the substitution of Ba for Caand Ks for Nas. It has been found 
in the Binnenthal, Switzerland, and at Jakobsberg, Sweden. 
A baryta- feldspar, having the ratio of andesite, 1:3:8, has been 
described which is ¢r iclinic, and approaches oligoclase i in optical char- 
acters. 
Oligoclase.—Soda-lime Feldspar. 
Triclinic. Angle between the cleavage planes 93° 50’ and 
86°10’. Commonly in cleavable masses. Also massive. 
Color usually white, grayish white, grayish gr ee, green- 
ish, reddish. Transparent, subtranslucent, H.=6-7. G.= 
2° 5. 2°, | 

