SUBSILICATES. 289 
Composition. H,Be,Al Oj, S8ip= Silica 41°20, alumina 35°22, 
-glucina 17°39, water 6:19=100. B.B. fuses with much dil- 
jiculty to a white enamel ; not acted on by acids. 
Diff. The cleavage of this glassy mineral is, like that of 
topaz, very perfect, “put is not basal. ‘The cleavage distin- 
guishes it from tourmaline and bery]. 
Obs. Occurs in the Ural, and with topaz in Brazil. 
The crystals of this mineral are elegant gems of them- 
selves, but they are seldom cut for jewelry on account of 
their brittleness. 
Datolite.—Datholite. Humboldtite. 
Monoclinic. Crystals without distinct cleavage ; small 
and glassy. Also botryoidal, 
with a columnar structure, 
and then called Jdotryolite. 
Color white, occasionally gray- 
ish, greenish, yellowish, or red- 
dish. Translucent, H.—5-5-5. 
G.=2°8-3.. 
Composition. H,Ca By Oy Sie 
=—oniea.o¢ a, boron, trioxide 
me lame. oo 0s. water d)6= 
100. Botryolite contains twice 
the proportion of water. B.b. 
becomes opaque, intumesces and melts easily to a glassy 
globule colormg the flame green. Decomposed by hydro- 
chloric acid ; the solution oelatinizes on evaporation. 
Dig. \ts elassy complex crystallizations, without cleavage, 
are unlike any other mineral that gelatinizes with acid. 
It is distinguished from minerals that it resembles also by. 
tingeing the blowpipe-flame green. : 
Obs Occurs in cavities in trap rocks and gneiss. Found 
in Scotland; at Andreasburg; at Baveno; Toggiana; also 
Bergen Hill, in N. J.; in Connecticut, at Roaring Brook, 
14 miles from New Haven; and near Hartford, Berlin, Mid- 
dlefield Falls, Conn.; also im great abundance at Eagle 
Harbor in the copper region, Lake Superior, and on Isle 
Royale ; also near Santa Clara, Cal, 


Homiiiie. A black silicate of iron and ealcium, resembling gadoli- 
nite, but affording from 15 to 18 per cent. of boracic acid with 32 of 
gilica ; formula RB, JB O,, Si, From Brevig, Norway, 
