SERPENTINE

Description:

Serpentine is a major rock forming mineral and is found as a constituent in many metamorphic and weather igneous rocks. Its colours range from white to grey, yellow to green, and brown to black, and are often splotchy or veined. Black Serpentine is unusual and an indication that the Serpentine minerals are particularly fine grained, dense and not reflective. Serpentine often colours rocks to a green colour and most rocks that have a green color probably have serpentine in some amount. The mineral occurs in metamorphosed and hydrothermally-altered ultra-basic rocks.

The name serpentine may come from the Latin word serpens, for "serpent." Some feel that the name "serpentine" is derived from the ancient belief that it cured a serpent's bite or because it resembled the dark green mottled variety of a serpent's skin.

The serpentine group contains several polytypes. These minerals are not always easy to individualize, and distinctions are not usually made. There are three important aggregate structures of serpentine.  Antigroite, which occurs in tough, compact, often pleated masses in shades of dark green (often schistose in formation as well). Chrysotile is almost always in fibrous yellowish-white or green aggregates. Lizardite is in minute scales or compact whitish aggregates. Most serpentines are opaque to translucent, light, soft, infusible and susceptible to acids. Non-fiberous serpentine is not a cancer concern. Asbestos serpentines should be kept in closed clear containers, but makes an attractive specimen. Soils derived from serpentine are toxic to many plants due to their high mineral content, and the flora is generally very distinctive, with specialised, slow-growing species.

Serpentine is found in the US, Canada, China, England, Russia, Italy and India. The California coastal ranges are essentially made up of large massive serpentine formations.

Serpentines find use in industry for a number of purposes, such as railway ballasts, building materials, and the asbesti-form types find use as thermal and electrical insulation (chrysotile asbestos). The more attractive and durable varieties (all of antigorite) are termed "noble" or "precious" serpentine and are used extensively as gems and in ornamental carvings. If dyed, they may imitate jade. Misleading synonyms for this material include "Korean jade", "Suzhou jade", "Styrian jade", and "New jade". New Caledonian serpentine is particularly rich in nickel, and is the source of most of the world's nickel ore. Sculpture is produced from a variety of Zimbabwean rocks, which have a diverse origin and geological history.

Characteristics:

Chemistry: (Mg,Fe)3Si2O5(OH)4, Magnesium Iron Silicate Hydroxide

Class: silicates

Hardness (Mohs scale): 2.5 – 4

Density: 2.2 – 2.9

Refractive index: 1.545 – 1.571

Crystal system: variable (monoclinic, trigonal, hexagonal or orthorhombic) depending on the

variety

Crystal habit: massive in habit, never being found as single crystals

Transparency: translucent to opaque

Luster: greasy, waxy or silky

Cleavage: in lizardite and antigorite is good in one direction

Fracture: conchoidal or splintery