196 DESCRIPTIONS OF MINERALS. 
colors from red to brown and black ; especially at Frank- 
lin, Newton and Sparta, in the former, and in Warwick, 
Amity and Edenville, in the latter. The crystals are octa- 
hedrons, and often grouped or disseminated singly in gran- 
ular limestone. One crystal, found at Amity by Dr. Heron, 
weighs 49 pounds. ‘he limestone quarries of Bolton, Box. 
borough, Chelmsford and Littleton, Mass., afford a few ~ 
crystals. 
Crystals of spinel are occasionally soft, having under- 
gone a change of composition approaching steatite in all 
characters except form. 'Theyare true psewdomorphs. They 
are met with in Sussex and Orange counties. Other spinel 
pseudomorphs consist of hydr otalcite (see preceding page). 
Uses. he fine colored spinels are much used as gems. 
The red is the common ruby of jewelry, the oriental rubies 
being sapphire. 
Gahnite is a spinel in which zinc takes the place of part or all of the 
magnesium; when all, it is called Automolite. Color dark green or green- 
ish black. H.=7:°5-8. G.=4-4°6. When fused with sufficient soda, 
B.B. on coal a white coat of zinc oxide is deposited, which is yellow 
when hot. B.B. infusible. At Franklin, N. J., and at the Canton 
mine in Georgia. Occurs in granite at Haddam with beryl, chryso- 
beryl,garnet, etc. In Sweden, near Fahlun, in talcose slate. 
Dysiuite. <A variety of gahnite containing oxide of manganese. 
Color yellowish or grayish-brown. H.=7'5 6. G.=4°55. Composi- 
tion, Alumina 80'5, zine oxide 16°8, iron sesquioxide 41°9, manganese 
protoxide 7'6, silica 3, water 0-4. From Sterling, N. J., with frank- 
linite and troostite. 
Kreittonite is a zine-iron gahnite. 
Hercinite is aspinel affording on analysis alumina and iron protoxide, 
with only 2:9 per cent. of magnesia, 
Chrysoberyl. 
Trimetric. JA /=129° 38’. Also in compound ervstals, 
as in fig. 7. Crystals sometimes thick ; often tabular. 
Color bright green, from a hght shade to emerald-green ; 
rarely raspberry or columbine-red by transmitted light. 
Streak uncolored. Lustre vitreous. ‘Transparent to trans- 
Incent. 9 H-=85 1G. ==3 92358: 
Composition. Be Al O, = Alumina 80:2, glucina 19°8=100. 
A little iron is sometimes present. B.B. infusible and un- 
altered. 
Alexandrite is an emerald-green variety from the Urals, 
colored by chrome, bearing the same relation to ordinary 
chrysoberyl as emerald to ‘beryl. Fig. 7 is of this variety. 
