At what depth olivine changes to spinel?
Answers
Answer:
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Explanation:
High-pressure polymorphs
Below depths of about 410 km (250 mi) olivine undergoes an exothermic phase transition to the sorosilicate, wadsleyite and, at about 520 km (320 mi) depth, wadsleyite transforms exothermically into ringwoodite, which has the spinel structure.
Category: Nesosilicate; Olivine group; Olivine series
Optical properties: Biaxial (+)
Crystal system: Orthorhombic
Crystal habit: Massive to granular
Answer:
Below depths of about 410 km (250 mi) olivine undergoes an exothermic phase transition to the sorosilicate, wadsleyite and, at about 520 km (320 mi) depth, wadsleyite transforms exothermically into ringwoodite, which has the spinel structure.
Category: Nesosilicate; Olivine group; Olivine ...
Optical properties: Biaxial (+)
Specific gravity: 3.2–4.5
Refractive index: nα = 1.630–1.650; nβ = 1.65...
Explanation:
he mineral olivine ( /ˈɒlɪˌviːn/) is a magnesium iron silicate with the formula (Mg2+, Fe2+)2SiO
4. Thus, it is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle,[8] it is a common mineral in Earth's subsurface, but weathers quickly on the surface.
The ratio of magnesium to iron varies between the two endmembers of the solid solution series: forsterite (Mg-endmember: Mg
2SiO
4) and fayalite (Fe-endmember: Fe
2SiO
4). Compositions of olivine are commonly expressed as molar percentages of forsterite (Fo) and fayalite (Fa) (e.g., Fo70Fa30). Forsterite's melting temperature is unusually high at atmospheric pressure, almost 1,900 °C (3,450 °F), while fayalite's is much lower — about 1,200 °C (2,190 °F). Melting temperature varies smoothly between the two endmembers, as do other properties. Olivine incorporates only minor amounts of elements other than oxygen (O), silicon (Si), magnesium (Mg) and iron (Fe). Manganese (Mn) and nickel (Ni) commonly are the additional elements present in highest concentrations.
Olivine in polarizing light
Olivine gives its name to the group of minerals with a related structure (the olivine group)—which includes tephroite (Mn2SiO4), monticellite (CaMgSiO4), larnite (Ca2SiO4) and kirschsteinite (CaFeSiO4) (commonly also spelled kirschteinite [9]).
Olivine's crystal structure incorporates aspects of the orthorhombic P Bravais lattice, which arise from each silica (SiO4) unit being joined by metal divalent cations with each oxygen in SiO4 bound to three metal ions. It has a spinel-like structure similar to magnetite but uses one quadrivalent and two divalent cations M22+ M4+O4 instead of two trivalent and one divalent cations.[10]
Olivine gemstones are called peridot and chrysolite.
Olivine rock is usually harder than surrounding rock and stands out as distinct ridges in the terrain. These ridges are often dry with little soil. Drought-resistant Scots pine is one of the few trees that thrive on olivine rock. Olivine pine forest is unique to Norway. It is rare and found on dry olivine ridges in the fjord districts of Sunnmøre and Nordfjord. Olivine rock is hard and base-rich.
Contents
1 Identification and paragenesis
1.1 Extraterrestrial occurrences
2 Crystal structure
3 High-pressure polymorphs
4 Weathering
5 Mining
5.1 Norway
6 Uses
7 See also
8 References
9 External links
Identification and paragenesis
Olivine grains that eroded from lava on Papakolea Beach, Hawaii
Light green olivine crystals in peridotite xenoliths in basalt from Arizona
Olivine basalt from the Moon, collected by the crew of Apollo 15