Serpentine

Serpentine is a group of silicate minerals, mainly composed of hydrated magnesium silicates. It generally displays green, yellow, brown, or black colors, often with veined or mottled textures.

It primarily forms through the hydrothermal alteration of magnesium-rich rocks, particularly peridotites.

Not to be confused with jade: serpentine is sometimes marketed as "jade" or "new jade," even though they are different minerals.