Serpentine

Serpentine is a group of related magnesium silicate minerals, principally antigorite, lizardite, and chrysotile, that share a similar chemistry and typically green, mottled appearance reminiscent of snakeskin (hence the name). The rock made largely of these minerals is called serpentinite.

Colors range from pale yellow-green to deep olive and brownish green, often with patchy or veined patterns and a smooth, sometimes greasy or waxy feel. Hardness varies widely across the group.

Serpentine is common worldwide and has long been used as a carving and ornamental stone. Some fine, translucent material (bowenite) is sold as "new jade." Note that chrysotile serpentine is the fibrous form historically mined as asbestos.

Serpentine forms by serpentinization, a metamorphic-hydrothermal process in which water reacts with magnesium- and iron-rich rocks from the Earth's mantle and oceanic crust, mainly peridotite and other ultramafic rocks. Hot fluids alter the original olivine and pyroxene minerals into serpentine-group minerals.

This occurs along mid-ocean ridges, in subduction zones, and where ultramafic bodies are tectonically emplaced into the crust. The resulting serpentinite is often found in fault zones and ophiolite complexes. Major occurrences include California, Italy, the UK (Cornwall, the Lizard Peninsula), Canada, China, and Afghanistan.

Look for a green to yellow-green mineral with a smooth, waxy to greasy luster, mottled or veined snakeskin patterning, and a relatively soft, easily scratched surface (hardness about 3-5.5, varying by variety).

It has a white streak, is translucent to opaque, and feels slightly slippery. The wide hardness range and lower density help separate it from true jade.

Look-alikes: nephrite and jadeite jade are harder (6-7) and tougher, so serpentine sold as "new jade" can be scratched more easily. Distinguish from green chalcedony (harder, hardness 7) and from green marble (fizzes in acid; serpentine does not). Fibrous chrysotile serpentine should be handled with care as it is an asbestos mineral.

Serpentine has long been carved into bowls, figurines, beads, cabochons, and architectural ornaments because it is soft, workable, and takes a good polish. Translucent bowenite is used in jewelry and sometimes passed off as jade. It has also been used as a decorative building and facing stone.

Industrially, magnesium-rich serpentine is a source of magnesium compounds, and historically chrysotile was the main source of asbestos, a use now heavily restricted for health reasons.

Metaphysically it is marketed as an earthy, heart-related stone for renewal and balance, though these claims are not scientific. Its main practical value is ornamental and as a magnesium ore.