Description
The mineral serpentine, or clinochrysotile, is a magnesium-iron silicate with the chemical formula (Mg, Fe)3Si2O5(OH)4. It belongs to the phyllosilicate family. This amorphous mineral can be red, yellow, white, and green. The green color is typical of the mineral in the mantle rock serpentinite. Its hardness is 2.5 to 4, depending on the composition, and serpentine has an average density of 2.59. One of these minerals is classified as asbestos. Inhalation of this mineral is harmful to health. The mineral serpentine, like the rock serpentinite, is named after the Latin word serpens, meaning "snake." The shape in which the minerals have grown within the rock is reminiscent of a snake. It was also used in the past as a remedy for snakebites. The other name for serpentinite, clinochrysotile, is derived from the Greek words clinos, chrysos, and tilos ("crooked," "gold," and "fiber," respectively). It is so named because of the gold-colored, fibrous structure the mineral can assume. Serpentine is an indicative mineral for serpentinite, a peridotite often converted by hydrothermal activity. Under the influence of pressure and temperature, the olivine and pyroxene from the mantle rock are converted into serpentine. This is sometimes called serpentinitization. The chemical reaction equation is: 4Mg2SiO4 (olivine) + 4H2O(l) + 2CO2(aq) → Mg6Si4O10(OH)8 (serpentine) + 2MgCO3 (magnesite) Serpentine is therefore a mineral found in areas where mantle rock has reached the surface, usually in orogens. Serpentine is widely exposed in Greece and the Alps.
Serpentine
The mineral olivine (peridot) is a nesosilicate with the chemical formula (Mg,Fe)2SiO4, where the end-members between magnesium and iron are formed by the mineral series forsterite (rich in Mg) and fayalite (rich in Fe). Olivine has an orthorhombic crystal system and crystallizes in a slightly oblate form, but can also occur as massive or granular. It fractures conchoidally and is somewhat brittle. The hardness of olivine ranges from 6.5 to 7. Its average density is 3.32 kg/l, and the mineral has a vitreous luster. It usually has an olive green color (hence the name), but it can also be reddish due to the oxidation of trivalent iron. It is transparent to translucent. Olivine occurs as a rock-forming mineral in mafic igneous rocks and in certain metamorphic rocks. It has also been discovered in meteorites and traced on Mars by the American Mars Odyssey space probe. The Mars Exploration Rovers have further confirmed its presence. Olivine is formed in magma rich in magnesium and poor in silicates (silicon dioxide). It is an important mineral in rocks such as gabbro, norite, the mantle rock peridotite (dunite), and as small crystals in basalt. The metamorphism of impure dolomite or other sedimentary rocks rich in magnesium and low in silicates also appears to form olivine. Olivine is a commonly used material for facade cleaning. Small olivine grains are blasted onto the wall with water to remove the contaminated layer. Olivine is more suitable for this than ordinary sand grains due to its greater hardness. Olivine has become a hot topic due to the current global intensive search for inexpensive processes to bind CO2 to minerals. Olivine is a basic rock. It reacts relatively quickly with the (acidic) CO2 in the atmosphere. Crushed olivine therefore weathers completely within a few years, depending on the grain size. To bind (neutralize) the CO2 produced by 1 liter of crude oil during combustion, slightly less than 1 liter of olivine is needed. The reaction is exothermic. The end products of the reaction are, depending on the composition of the olivine, magnesium carbonate or silicon oxide (sand)
