Forsterite
Forsterite (peridot) crystal captured in space by NASA's Stardust spacecraft. Peridot (pronunciation /ˈpɛrɪˌdɒt/, /ˈpɛrɪˌdoʊ/ (British English /ˈpɛərɪˌdɑt/ /ˈpɛərɪˌdɑʊ/ (US English is the gem quality variety of forsteritic The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program Stardust is an American interplanetary mission of the NASA Jet Propulsion Laboratory, whose primary purpose was to investigate the makeup of the
General
Category	Silicate mineral
Chemical formula	Magnesium silicate (Mg2SiO4)
Identification
Color	Colorless, green, yellow, yellow green, white
Crystal habit	Dipyramidal prisms often tabular, commonly granular or compact massive
Crystal system	Orthorhombic
Twinning	On {100}, {011} and {012}
Cleavage	Perfect on {010} imperfect on {100}
Fracture	Conchoidal
Mohs Scale hardness	7
Luster	Vitreous
Refractive index	nα = 1. The silicate minerals make up the largest and most important class of rock-forming Minerals They are classified based on the structure of their silicate Ion group A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 For the Artificial intelligence Androids of the 1990s Science fiction series Space Above and Beyond, see Silicate (AI Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the In Mineralogy, shape and size give rise to descriptive terms applied to the typical appearance or habit of Crystals The many terms used by mineralogists A crystal system is a category of Space groups which characterize Symmetry of structures in three dimensions with Translational symmetry in three directions In Crystallography, the orthorhombic Crystal system is one of the seven Lattice Point groups Orthorhombic lattices result from stretching Crystal twinning occurs when two separate crystals share some of the same Crystal lattice points in a symmetrical manner Cleavage, in Mineralogy, is the tendency of crystalline materials to split along definite planes creating smooth surfaces of which there are several named types In the field of Mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a Mineral is broken The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material Lustre (or luster) is a description of the way light interacts with the surface of a Crystal, rock, or Mineral. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium 636 - 1. 730 nβ = 1. 650 - 1. 739 nγ = 1. 669 - 1. 772
Optical Properties	Biaxial (+)
Birefringence	δ = 0. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray 033 - 0. 042
Streak	White
Specific gravity	3. The streak (also called powder color) of a Mineral is the Color of the powder produced when it is dragged across an unweathered surface Specific gravity is defined as the ratio of the Density of a given solid or liquid substance to the density of water at a specific temperature and pressure typically 21 - 3. 33
Melting point	1890 °C[1]
Diaphaneity	Transparent to translucent
References	[2][3][4]

Forsterite (Mg₂SiO₄) is the magnesium rich end-member of the olivine solid solution series. The melting point of a solid is the temperature range at which it changes state from solid to Liquid. The Mineral olivine (when gem-quality also called Peridot) is a Magnesium Iron silicate with the formula ( Mg A solid solution is a Solid - state Solution of one or more solutes in a Solvent. Forsterite crystallizes in the orthorhombic system (space group Pbnm) with cell parameters a 4. In Crystallography, the orthorhombic Crystal system is one of the seven Lattice Point groups Orthorhombic lattices result from stretching The space group of a Crystal or crystallographic group is a mathematical description of the Symmetry inherent in the structure 75 Å (0. An ångström or angstrom (symbol Å) (ˈɔːŋstrəm Swedish: ˈɔ̀ŋstrœm is an internationally recognized non- SI unit of length equal 475 nm), b 10. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a 20 Å (1. 020 nm) and c 5. 98 Å (0. 598 nm). ^[1]

Forsterite is associated with igneous and metamorphic rocks and has also been found in meteorites. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change A meteorite is a natural object originating in Outer space that survives an impact with the Earth 's surface In 2005 it was also found in cometary dust returned by the Stardust probe. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — Stardust is an American interplanetary mission of the NASA Jet Propulsion Laboratory, whose primary purpose was to investigate the makeup of the ^[5]

Peridot is the gemstone variety of forsterite olivine. Peridot (pronunciation /ˈpɛrɪˌdɒt/, /ˈpɛrɪˌdoʊ/ (British English /ˈpɛərɪˌdɑt/ /ˈpɛərɪˌdɑʊ/ (US English is the gem quality variety of forsteritic A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash

Forsterite reacts with quartz to form the orthopyroxene mineral enstatite in the following reaction:

Mg₂SiO₄ + SiO₂ → 2MgSiO₃. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in The pyroxenes are a group of important rock-forming Silicate minerals found in many Igneous and metamorphic rocks. Enstatite is the magnesium endmember of the Pyroxene Silicate mineral series enstatite (MgSiO3 - ferrosilite (FeSiO3

Composition

Pure forsterite is composed of magnesium, oxygen and silicon. The chemical formula is Mg₂SiO₄. Forsterite and fayalite (Fe₂SiO₄) are the endmembers of the olivine solid solution series; other elements such as Mn, Ni, and Ca substitute for Fe and Mg in olivine, but only in minor proportions in natural occurrences. Other minerals such as monticellite (CaMgSiO₄), an uncommon calcium-rich mineral, share the olivine structure, but solid solution between olivine and these other minerals is limited. Monticellite and kirschsteinite are Gray Silicate Minerals of the Olivine group with compositions Ca[[magnesium Mg]] Monticellite is found in contact metamorphosed dolomites. Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i Dolomite (ˈdɒləmaɪt is the name of a Sedimentary Carbonate rock and a Mineral, both composed ^[1]

Geologic occurrence

Forsterite-rich olivine is the most abundant mineral in the mantle above a depth of about 400 km; pyroxenes are also important minerals in this upper part of the mantle. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided ^[6] Although pure forsterite does not occur in igneous rocks, dunite often contains olivine with forsterite contents at least as Mg-rich as Fo₉₂ (92% forsterite - 8% fayalite); common peridotite contains olivine typically at least as Mg-rich as Fo₈₈. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock Dunite (ˈduːnaɪt or /ˈdʌnaɪt/ is an igneous, Plutonic rock, of Ultramafic composition with coarse-grained or Phaneritic A peridotite is a dense coarse-grained Igneous rock, consisting mostly of the minerals Olivine and Pyroxene. ^[7] Forsterite-rich olivine is a common crystallization product of mantle-derived magma. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet Olivine in mafic and ultramafic rocks typically is rich in the forsterite endmember.

Forsterite also occurs in dolomitic marble which results from the metamorphism of high magnesium limestones and dolostones. Marble is a nonfoliated Metamorphic rock resulting from the Metamorphism of Limestone, composed mostly of Calcite (a crystalline form of Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Dolostone is a sedimentary Carbonate rock that contains a high percentage of the Mineral Dolomite. ^[8] Nearly pure forsterite occurs in some metamorphosed serpentinites. Serpentinite is a rock composed of one or more Serpentine Minerals Minerals in this group are formed by serpentinization a hydration and metamorphic Fayalite-rich olivine is much less common. Nearly pure fayalite is a minor constituent in some granite-like rocks, and it is a major constituent of some metamorphic banded iron formations. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Banded iron formations (also known as banded ironstone formations or BIF s are a distinctive type of rock often found in primordial ( Precambrian) Sedimentary

Structure and formation

Forsterite is mainly composed of the anion SiO^2-₄ and the cation Mg²⁺. ^[9] Silicon is the central atom in the SiO^2-₄ anion. Each oxygen atom is bonded to the silicon by a single covalent bond. The four oxygens have a partial negative charge because of the covalent bond with silicon. Therefore, oxygens need to stay far from each other in order to reduce the repulsive force between them. The best geometry to reduce the repulsion is a tetrahedral shape. The cations occupy two different octahedral sites which are M1 and M2 and form ionic bonds with the silicate molecules. M1 and M2 are slightly different. M2 site is larger and more regular than M1 as shown in fig. 1. The packing in forsterite structure is dense. The space group of this structure is Pbnm and the point group is 2/m 2/m 2/m which is an orthorhombic crystal structure.

FIG. 1: Forsterite Structure ( See Klein 23rd FIG 18. 4 Pg 439)

This structure of forsterite can form a complete solid solution by replacing the magnesium with iron. A solid solution is a Solid - state Solution of one or more solutes in a Solvent. ^[10] Iron can form two different cations which are Fe²⁺ and Fe³⁺. The iron(II) ion has the same charge as magnesium ion and it has a very similar ionic radius to magnesium. Consequently, Fe²⁺ can replace the magnesium ion in the olivine structure.

One of the important factors that can increase the portion of forsterite in the olivine solid solution is the ratio of iron(II) ions to iron(III) ions in the magma. ^[11] As the iron(II) ions oxidize and become iron(III) ions, iron(III) ions can not form olivine because of their positive three charge. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state The occurrence of forsterite due to the oxidation of iron was observed in the Stromboli volcano in Italy. Stromboli (Strongyle is a small island in the Tyrrhenian Sea, off the north coast of Sicily, containing one of the three active volcanoes in Italy Plate tectonics and hotspots Divergent plate boundaries At the As the volcano fractured, gases and volatiles escaped from the magma chamber. The crystallization temperature of the magma increased as the gases escaped. Because iron(II) ions were oxidized in the Stromboli magma, little iron(II) was available to form olivine. Hence, the crystallizing olivine was Mg-rich, and igneous rocks rich in forsterite were formed.

Discovery and name

Forsterite was first described in 1824 for an occurrence at Mte. Somma, Vesuvius, Italy. It was named by Armand Lévy in 1824 for the English naturalist and mineral collector Jacob Forster. ^[12][13]

References

1. ^ ^{a b c} Klein, Cornelis and Cornelius Hurlbut Jr. , 1985, Manual of Mineralogy, 20th ed. , Wiley, p 373-375 ISBN 0-471-80580-7
2. ^ http://rruff.geo.arizona.edu/doclib/hom/forsterite.pdf
3. ^ Forsterite: Forsterite mineral information and data
4. ^ Forsterite Mineral Data
5. ^ Lauretta, Ds, Keller, LP, & Messenger, S. (2005). Supernova Olivine from Cometary Dust. Science, 309, 737-741
6. ^ Kushiro, I. The System Forsterite- Diopside- Silica with and without Water at High Pressure, American Journal of Science, 267, 269-294
7. ^ Deer, W. A. , Howie, R. A. , and Zussman, J. (1992). An introduction to the rock-forming minerals (2nd ed. ). Harlow: Longman ISBN 0-582-30094-0
8. ^ Tormmsdof, V. (1966). Progressive Metamorphose kieseliger Karbonatgesteine in den Zentralalpen zwischen Bernina und Simplon. Schweizerische Mineralogische und Petrographische Mitteilungen = Bulletin Suisse de Mineralogie et Petrographie, 46, 431-460
9. ^ Iishi, K. (1978). Lattice Dynamics of Forsterite. American Mineralogist, 63, 1198 - 1208
10. ^ Keppla, O. J, & Wood, B. J. Thermochemistry of forsterite- fayalite olivine solutions. Geochimica et Cosmochimica Acta, 45, 529- 534
11. ^ Wilson, M, Condliffe, E, Cortes, J. A, & Francalanci, L. (2006). The Occurrence of Forsterite and Highly oxidizing conditions in Basaltic Lavas from Stromboli Volcano, Italy. Journal of Petrology, 47, 1345- 1373
12. ^ Frondel, C. (1972). Jacob Forster (1739- 1806) and his connections with forsterite and palladium. Mineralogy Magazine, 38, 545- 550 Available in PDF form at: http://www.minersoc.org/pages/Archive-MM/Volume_38/38-297-545.pdf
13. ^ http://minrec.org/labels.asp?colid=726 Mineralogical Record, Biographical Archive