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Serpentine soils are soils derived from ultramafic rocks, in particular serpentinite, an ultramafic rock formed by the a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle. The soils derived from ultramafic bedrock give rise to unusual and sparse associations of edaphic plants that are tolerant of extreme soil conditions such as a low calcium-magnesium ratio, lack of essential nutrients such as nitrogen, potassium, and phosphorus, and high concentrations of the heavy metals that are more common in ultramafic rocks. These plants are commonly called serpentine endemics, if they grow only on these soils. (Serpentinite is comprised of the mineral serpentine, but the two terms are often both used to mean the rock, not its mineral composition.)
In areas where these ultramafic rocks are patchy, such as the Klamath Basin region, the areas of serpentine soil can be clearly seen as sparsely covered areas bounded by forest on the normal soils. Areas of serpentine soil are also home to diverse wildflowers, many of which are rare or endangered species such as Acanthomintha duttonii and Pentachaeta bellidiflora.
Serpentine rock has a mottled, greenish-gray color with a waxy feel to it. These rocks form when the upper mantle of the earth's crust containing wet oceanic sediments is submerged under a land mass, which results in the chemical addition of water to heavy mantle rock. The serpentine rock is softer and thus more slippery, giving it the ability to work its way upward along fault lines, it moves itself between other rock layers while under pressure and is exposed to the surface during mountain uplifts. Although it covers only about 1 percent of the state's surface, the state rock of California is serpentine.