Serpentinite

Serpentinite is a metamorphic rock composed largely of serpentine-group minerals (antigorite, lizardite, and chrysotile). It typically forms attractive mottled green masses, sometimes streaked with white veins or black magnetite, giving it a marbled, snakeskin-like appearance that inspired its name.

The rock is relatively soft, often feels smooth, greasy, or waxy, and takes a good polish. It is the dominant rock of the Earth's altered oceanic mantle and is commonly found in ophiolite complexes where slices of seafloor have been thrust onto continents.

Serpentinite is California's official state rock and is widely used as a decorative and carving stone, frequently marketed under the name serpentine.

Serpentinite forms through serpentinization, a process in which water reacts with magnesium- and iron-rich ultramafic rocks such as peridotite and dunite from the Earth's mantle. This hydration alters olivine and pyroxene into serpentine minerals, releasing heat and dramatically changing the rock's volume and density.

The process occurs primarily at mid-ocean ridges and along subduction zones where seawater penetrates the oceanic crust and uppermost mantle. When ocean floor is later obducted onto continents as ophiolites, the serpentinite is exposed. Major occurrences include California, the Alps, Cyprus, Italy, and New Zealand.

Identify serpentinite by its green to dark-green color, often mottled or veined, and its characteristically smooth, waxy, or soapy feel. It is soft enough to scratch with a knife and frequently shows a slightly translucent, greasy luster on cut surfaces.

Its streak is white. Look-alikes include jade (nephrite and jadeite), which is much harder and tougher, and soapstone, which is even softer and dominated by talc. Marble is harder than typical serpentinite and fizzes in acid, whereas serpentinite does not react. Some serpentinite contains fibrous chrysotile (a form of asbestos), so handle dusty or fibrous specimens with care.

Serpentinite is widely used as an ornamental and architectural stone for tiles, countertops, and facing slabs, often sold as 'green marble' or verd antique. Its softness makes it popular for carving figurines, bowls, and beads.

In the gem and metaphysical trade, attractive translucent varieties are cut as 'new jade' or 'healerite.' Industrially, magnesium-rich serpentinite is a source of magnesium and is studied for carbon sequestration. Historically chrysotile serpentinite was mined for asbestos, an application now largely abandoned for health reasons. Metaphysically it is associated with earth connection and healing, though such claims are not scientifically verified.