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Optical properties of common minerals Name Crystal system Indicatrix Optical sign ... Olivine: Orthorhombic: Biaxial (-) or (+) 0.042: Colorless to pale green Orthoclase:
The mineral olivine (/ ˈ ɒ l. ɪ ˌ v iː n /) is a magnesium iron silicate with the chemical formula (Mg,Fe) 2 Si O 4.It is a type of nesosilicate or orthosilicate.The primary component of the Earth's upper mantle, [9] it is a common mineral in Earth's subsurface, but weathers quickly on the surface.
Orange forsterite with a portion of tephroite. Pure forsterite is composed of magnesium, oxygen and silicon. The chemical formula is Mg 2 SiO 4.Forsterite, fayalite (Fe 2 SiO 4) and tephroite (Mn 2 SiO 4) are the end-members of the olivine solid solution series; other elements such as Ni and Ca substitute for Fe and Mg in olivine, but only in minor proportions in natural occurrences.
Iddingsite is a rock that lacks a definite chemical composition, so exact compositions cannot be calculated. An approximated composition for a hypothetical end product of iddingsite has been calculated as being SiO 2 = 16%, Al 2 O 3 = 8%, Fe 2 O 3 = 62% and H 2 O = 14%.
Fayalite (Fe 2 SiO 4, commonly abbreviated to Fa) is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system (space group Pbnm) with cell parameters a 4.82 Å, b 10.48 Å and c 6.09 Å.
Clinohumite is an uncommon member of the humite group, a magnesium silicate according to the chemical formula (Mg, Fe) 9 (Si O 4) 4 (F,OH) 2.The formula can be thought of as four olivine (Mg 2 SiO 4), plus one brucite (Mg(OH) 2).
Diopside is found in ultramafic (kimberlite and peridotite) igneous rocks, and diopside-rich augite is common in mafic rocks, such as olivine basalt and andesite. Diopside is also found in a variety of metamorphic rocks, such as in contact metamorphosed skarns developed from high silica dolomites .
The chemical reaction turns olivine into serpentine minerals. They may also have their origins in metamorphic alterations of peridotite and pyroxene. Serpentines may also pseudomorphously replace other magnesium silicates. Incomplete alteration causes the physical properties of serpentines to vary widely.