7O MINERALOGY AND LITHOLOGY. 
46. CurysoLiTEe (OxIvine) [(Mg, Fe), Si Oy]. 
This mineral is a prominent ingredient of some of our igneous rocks. 
It was first noticed as an ingredient of the trap at Campton falls by 
Prof. O. P. Hubbard,* who also found it forming masses of some size 
in a very coarsely crystalline diabase, which is found in boulders (the 
original locality for which is not known) at Thetford, Vt. It was ident- 
ified in the gabbro from Waterville + by Mr. E.S. Dana. When visible to 
the eye in the rocks it has a vitreous lustre, and a greenish yellow color. 
The easy decomposition to which it is subject makes it conspicuous; 
and rocks like our gabbros, which, when broken, show the clearest and 
freshest grains of chrysolite on a fresh fracture, are externally covered 
with iron-stained pits, from which the chrysolite has rotted away. It has 
been found, also, in granite boulders near the Crawford house. 
The following is an analysis of the chrysolite from the Waterville 
rock, by Mr. Dana. 
Silica, . 5 3 ‘ ‘ 5 és . ; . 7 - 38.85 
Alumina, . ‘ ‘ 7 F ‘ ‘ F 2 F @ : trace. 
Iron protoxide, , 3 i ; , P . . . : 28.07 
Manganese protoxide, . . ‘ . ‘ E a . 1.24 
Lime, . 7 ‘ . F e . - 7 . ‘i 1.43 
Magnesia, : ‘ : ‘ ; we t% ‘ 2 - 30.62 
100.21 
The analysis shows this to be the variety of chrysolite which com- 
monly occurs in rocks, and which is usually called olivine. It contains 
an unusually large amount of iron,—as remarked by Mr. Dana, the pro- 
portion between the iron and magnesia being as 1:2. Hence the 
formula for this olivine is 
ies ot 
When present in sections of rocks prepared for microscopic study, 
chrysolite is easily recognized. When crystalized, its sections are either 
six- or eight-sided, the figures being the sections of the most common 
form of the crystals of this species. This form is made by a combina- 
tion of two prisms and a macro- and brachydome. In the rocks that I 
have examined, the sections at right angles to the vertical axis appear 
* Am, Four. Science, i, vol. xxxiv, p. r10. + Id., iii, vol. iii, p. 48. 
