Serpentine Composition, Crystallization & Structure
Composition. A magnesium silicate, H4mMg3Sio9 = Silica 44.4, magnesia 43.0, water 12.9. Ferrous iron and nickel may be present in small amount.
Crystallization. Moclinic (optically). Occurs however, only in pseudomorphic crystals.
Structure. Often in delicate fibers, which can be separated from each other. Usually massive, but microscopically fibrous and felted.
Physical Properties. H. = 2.5-2.65. luster greasy, warlike in the massive varieties, silky when fibrous. Color olive to blackish green, yellowish green, white. Color often variegated, showing mottling in lighter and darkled shades of green. Translucent to opaque.
Test. Infusible. Decomposed by hydrochloric acid with the separation of silica but without the formation of a jelly. Filtered solution, after being oxidized with nitric acid and having any iron precipitated by ammonium hydroxide, and the absence of calcium proved by addition of ammonium oxalate, gives a precipate of ammonium-magnesium phosphate with sodium phosphate. Water in C. T. Recognized by its variegated green color and its greasy luster or by its fibrous structure.
Varieties. In crystals. Occurs in crystals as pseudomorphs after various magnesium silicates, principally chrysolie, pyroxene, amphibole.
- Precious Serpenatine. Massive, translucent, of light to dark green color. Often mixed with white marble and shows beautiful variegated coloring. Frequently called verd antique marble.
- Ordinary Serpentine. Massive, opaque, of various shades of green.
- Chrysotile. The fibrous asbestiform variety, which is to be found in veins traversing the massive serpentine. This is the asbestos of commerce for the most part.
Occurrence. A common mineral and widely distributed. Always as an alteration product of some magnesium silicate, especially chrysolite, also pyroxene, amphibole, ete. Frequently associated with magnesite, chrysolite, chromite, ete. Found in both igneous and metamorphie rocks, sometimes in disseminated particles, sometimes in such quantity as to make up practically the entire rock-mass. Precious serpentine is found at many localities. The fibrous variety, chrysotile, comes from the Province of Quebec, Canada, just north of the Vermont line; from Vermont; New York; New Jersey; in Arizona near Globe, from the Sierra Ancha and in the Grand Canyon.
Name. The name refers to the green serpent-like clouding of the massive variety.
Use. The variety chrysotile is the chief source of asbestos. Fibrous amphibole (which see) is also used for the same purposes. The uses of asbestos depend upon its fibrous, flexible structure, which allows it to be woven into cloth, felt, etc., and upon its incombustibility and slow conductivity of heat. Asbestos products, therefore, are used for fireproofing and as an insulating material against heat and electricity. The massive mineral is often used as an ornamental stone and may at times be valuable as building material.
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