Serpentine is a family of silicate minerals rich in magnesium and water, derived from low-temperature alteration or metamorphism of the minerals in ultramafic rocks.
Rocks made up of serpentine minerals are called serpentinite. These rocks are Igneous rocks. Igneous rocks are formed from melted rock that has cooled and solidified.
Serpentine minerals are light to dark green, commonly varied in hue, and greasy looking; the mineral feels slippery. (Credit: U.S. Geological Survey)