MINERALS. 
307 
FELDSPAR. 
Crystals of feldspar occur in San Diego county, in the granite veins along the road between 
Santa Isabel and San Pasqual, and are associated with tourmalines and garnets. Large and 
tolerably perfect crystals can be obtained from some of the coarse feldspatbic veins. It is 
probable that they will also be found in the similar coarse veins traversing the metamorphic 
rocks on the eastern or Gulf side of the chain. 
BRONZITE. 
The crystals occurring abundantly in the serpentinoid rocks of Fort Point; at the Orphan 
Asylum, and on the summit of Mount Diablo, are referred to the species bronzite or diallage. 
It is most distinctly developed at the locality on Mount Diablo, where it forms great rocky 
masses of confused crystals. In the serpentine near San Francisco, the crystals are isolated in 
the mass of the rock, and their broad and tabular cleavage faces are exposed when the rock is 
broken. On exhibiting the specimen from Mount Diablo to Professor Charles U. Shepard, he 
assured me that it bore the closest resemblance to the bronzite of Bacher Mount, Styria, occurring 
with serpentine. 
Diallage and bronzite are varieties of pyroxene or angite, and are associated with serpentine 
in New England and Europe. An analysis of a Greenland specimen of bronzite by Kobell 
yielded: 1 
•Silica... — ...... 58.00 
Magnesia...... 29.66 
Protoxide of iron _______ 10.14 
Manganese..... 1.00 
Alumina_ 1. 33 
An analysis of the California mineral is very desirable. 
CHRYSOTILE. 
Chrysotile occurs in the serpentine near San Francisco and at New Almaden, forming thin 
seams resembling amianthus or asbestos. It is seen standing out slightly above the surface of 
some weather-worn masses, covering them with lines like the reticulations of a net. The seams, 
so far as observed, are very thin, and do not furnish good cabinet specimens. The mineral is 
believed to have the composition of serpentine, and is a fibrous variety. It may, however, prove 
to be fibrous augite or amianthus. An analysis of a specimen of chrysotile from New Haven, 
Conn., by Professor George J. Brush, yielded: 2 
Silica........... 44.05 
Magnesia__...._. 39. 24 
Protoxide of iron___*._ 2.53 
Water............... 13, 49 
GYPSUM. 
Thin transparent plates of selenite are common in the soft, unconsolidated, sedimentary forma¬ 
tions in various parts of the State. In some localities it occurs abundantly, and the seams are 
many inches thick. These seams or layers are generally conformable with the stratification ; 
and some observations upon their origin are already presented in Chapter XIII. This mineral 
1 Journal fur pratische Chemie, Ch. xxxvi, 303. Cited in Dana’s Mineralogy, 4th ed., p. 162. 
8 Dana’s Mineralogy, 4th ed., II, p. 283. 
