|Category|| Nesosilicate |
| Formula |
|Color||Yellow to yellow-green|
|Crystal habit||Massive to granular|
|Fracture||Conchoidal – brittle|
|Mohs scale hardness||6.5–7|
|Diaphaneity||Transparent to translucent|
|Optical properties||Biaxial (+)|
|Refractive index||nα = 1.630–1.650 |
nβ = 1.650–1.670
nγ = 1.670–1.690
|Birefringence||δ = 0.040|
The mineral olivine ( // ) is a magnesium iron silicate with the formula (Mg 2+, Fe 2+)2 Si O 4. Thus it is a type of nesosilicate or orthosilicate. It is a common mineral in Earth's subsurface but weathers quickly on the surface.
A mineral is, broadly speaking, a solid chemical compound that occurs naturally in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are usually excluded, but some minerals are often biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings often syntesize inorganic minerals that also occur in rocks.
Magnesium is a chemical element with symbol Mg and atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column of the periodic table: all group 2 elements have the same electron configuration in the outer electron shell and a similar crystal structure.
Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series. It is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. Its abundance in rocky planets like Earth is due to its abundant production by fusion in high-mass stars, where it is the last element to be produced with release of energy before the violent collapse of a supernova, which scatters the iron into space.
The ratio of magnesium to iron varies between the two endmembers of the solid solution series: forsterite (Mg-endmember: Mg 2 Si O 4) and fayalite (Fe-endmember: Fe 2 Si O 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, silicon, magnesium and iron. Manganese and nickel commonly are the additional elements present in highest concentrations.
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a multi-component system is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the chemical components remain in a single homogeneous phase. This often happens when the two elements involved are close together on the periodic table; conversely, a chemical compound generally results when two metals involved are not near each other on the periodic table.
Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite. Forsterite crystallizes in the orthorhombic system (space group Pbnm) with cell parameters a 4.75 Å (0.475 nm), b 10.20 Å (1.020 nm) and c 5.98 Å (0.598 nm).
Silicon is a chemical element with symbol Si and atomic number 14. It is a hard and brittle crystalline solid with a blue-grey metallic lustre; and it is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic table: carbon is above it; and germanium, tin, and lead are below it. It is relatively unreactive. Because of its high chemical affinity for oxygen, it was not until 1823 that Jöns Jakob Berzelius was first able to prepare it and characterize it in pure form. Its melting and boiling points of 1414 °C and 3265 °C respectively are the second-highest among all the metalloids and nonmetals, being only surpassed by boron. Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earth's crust. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. More than 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust after oxygen.
Olivine gives its name to the group of minerals with a related structure (the olivine group)—which includes tephroite (Mn 2SiO4), monticellite (CaMgSiO4) and kirschsteinite (CaFeSiO4).
Tephroite is the manganese endmember of the olivine group of nesosilicate minerals with the formula Mn2SiO4. A solid solution series exists between tephroite and its analogues, the group endmembers fayalite and forsterite. Divalent iron or magnesium may readily replace manganese in the olivine crystal structure.
Manganese is a chemical element with symbol Mn and atomic number 25. It is not found as a free element in nature; it is often found in minerals in combination with iron. Manganese is a metal with important industrial metal alloy uses, particularly in stainless steels.
Monticellite and kirschsteinite are gray silicate minerals of the olivine group with compositions CaMgSiO4 and CaFeSiO4, respectively. Most monticellites have the pure magnesium end-member composition but rare ferroan monticellites and magnesio-kirschsteinite are found with between 30 and 75 mol.% of the iron end member. Pure kirschsteinite is only found in synthetic systems. Monticellite is named after Teodoro Monticelli Italian mineralogist (1759–1845).
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 3 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.
In geometry and crystallography, a Bravais lattice, named after Auguste Bravais (1850), is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by:
Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4 in the cubic crystal system. Its name comes from Latin "spina" (arrow). Balas ruby is an old name for a rose-tinted variety of spinel.
Olivine gemstones are called peridot and chrysolite.
A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks and occasionally organic materials that are not minerals are also used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone.
Peridot ( or ) (sometimes called chrysolite) is gem-quality olivine and a silicate mineral with the formula of (Mg, Fe)2SiO4. As peridot is a magnesium-rich variety of olivine (forsterite), the formula approaches Mg2SiO4.
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 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. The habitat is endangered by mining and road construction.
Olivine is named for its typically olive-green color (thought to be a result of traces of nickel), though it may alter to a reddish color from the oxidation of iron.
Translucent olivine is sometimes used as a gemstone called peridot (péridot, the French word for olivine). It is also called chrysolite (or chrysolithe, from the Greek words for gold and stone). Some of the finest gem-quality olivine has been obtained from a body of mantle rocks on Zabargad Island in the Red Sea.
Olivine occurs in both mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks. Mg-rich olivine crystallizes from magma that is rich in magnesium and low in silica. That magma crystallizes to mafic rocks such as gabbro and basalt. Ultramafic rocks such as peridotite and dunite can be residues left after extraction of magmas, and typically they are more enriched in olivine after extraction of partial melts. Olivine and high pressure structural variants constitute over 50% of the Earth's upper mantle, and olivine is one of the Earth's most common minerals by volume. The metamorphism of impure dolomite or other sedimentary rocks with high magnesium and low silica content also produces Mg-rich olivine, or forsterite.
Fe-rich olivine is relatively much less common, but it occurs in igneous rocks in small amounts in rare granites and rhyolites, and extremely Fe-rich olivine can exist stably with quartz and tridymite. In contrast, Mg-rich olivine does not occur stably with silica minerals, as it would react with them to form orthopyroxene ((Mg,Fe)2Si2O6).
Mg-rich olivine is stable to pressures equivalent to a depth of about 410 km (250 mi) within Earth. Because it is thought to be the most abundant mineral in Earth’s mantle at shallower depths, the properties of olivine have a dominant influence upon the rheology of that part of Earth and hence upon the solid flow that drives plate tectonics. Experiments have documented that olivine at high pressures (e.g. 12 GPa, the pressure at depths of about 360 km (220 mi)) can contain at least as much as about 8900 parts per million (weight) of water, and that such water contents drastically reduce the resistance of olivine to solid flow; moreover, because olivine is so abundant, more water may be dissolved in olivine of the mantle than contained in Earth's oceans.
Mg-rich olivine has also been discovered in meteorites,on the Moon and Mars, falling into infant stars, as well as on asteroid 25143 Itokawa. Such meteorites include chondrites, collections of debris from the early Solar System; and pallasites, mixes of iron-nickel and olivine.
The spectral signature of olivine has been seen in the dust disks around young stars. The tails of comets (which formed from the dust disk around the young Sun) often have the spectral signature of olivine, and the presence of olivine was verified in samples of a comet from the Stardust spacecraft in 2006.Comet-like (magnesium-rich) olivine has also been detected in the planetesimal belt around the star Beta Pictoris.
Minerals in the olivine group crystallize in the orthorhombic system (space group Pbnm) with isolated silicate tetrahedra, meaning that olivine is a nesosilicate. In an alternative view, the atomic structure can be described as a hexagonal, close-packed array of oxygen ions with half of the octahedral sites occupied with magnesium or iron ions and one-eighth of the tetrahedral sites occupied by silicon ions.
There are three distinct oxygen sites (marked O1, O2 and O3 in figure 1), two distinct metal sites (M1 and M2) and only one distinct silicon site. O1, O2, M2 and Si all lie on mirror planes, while M1 exists on an inversion center. O3 lies in a general position.
At the high temperatures and pressures found at depth within the Earth the olivine structure is no longer stable. 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. At a depth of about 660 km (410 mi), ringwoodite decomposes into silicate perovskite ((Mg,Fe)SiO3) and ferropericlase ((Mg,Fe)O) in an endothermic reaction. These phase transitions lead to a discontinuous increase in the density of the Earth's mantle that can be observed by seismic methods. They are also thought to influence the dynamics of mantle convection in that the exothermic transitions reinforce flow across the phase boundary, whereas the endothermic reaction hampers it.
The pressure at which these phase transitions occur depends on temperature and iron content. 800 °C (1,070 K; 1,470 °F), the pure magnesium end member, forsterite, transforms to wadsleyite at 11.8 gigapascals (116,000 atm ) and to ringwoodite at pressures above 14 GPa (138,000 atm). Increasing the iron content decreases the pressure of the phase transition and narrows the wadsleyite stability field. At about 0.8 mole fraction fayalite, olivine transforms directly to ringwoodite over the pressure range 10.0 to 11.5 GPa (99,000–113,000 atm). Fayalite transforms to Fe
4 spinel at pressures below 5 GPa (49,000 atm). Increasing the temperature increases the pressure of these phase transitions.
Olivine is one of the weaker common minerals on the surface according to the Goldich dissolution series. It alters into iddingsite (a combination of clay minerals, iron oxides and ferrihydrites) readily in the presence of water.Artificially increasing the weathering rate of olivine e.g. by dispersing fine-grained olivine on beaches has been proposed as a cheap way to sequester CO2. The presence of iddingsite on Mars would suggest that liquid water once existed there, and might enable scientists to determine when there was last liquid water on the planet.
Norway is the main source of olivine in Europe, particularly in an area stretching from Åheim to Tafjord, and from Hornindal to Flemsøy in the Sunnmøre district. There is also olivine in Eid municipality. About 50 % of the world's olivine for industrial use is produced in Norway. At Svarthammaren in Norddal olivine was mined from around 1920 to 1979, with a daily output up to 600 metric tons. Olivine was also obtained from the construction site of the hydro power stations in Tafjord. At Robbervika in Norddal municipality an open-pit mine has been in operation since 1984. The characteristic red color is reflected in several local names with "red" such as Raudbergvik (Red rock bay) or Raudnakken (Red ridge).
Hans Strøm in 1766 described the olivine's typical red color on the surface and the blue color within. Strøm wrote that in Norddal district large quantities of olivine were broken from the bedrock and used as sharpening stones.
Kallskaret near Tafjord is a nature reserve with olivine.
A worldwide search is on for cheap processes to sequester CO2 by mineral reactions, called enhanced weathering. Removal by reactions with olivine is an attractive option, because it is widely available and reacts easily with the (acid) CO2 from the atmosphere. When olivine is crushed, it weathers completely within a few years, depending on the grain size. All the CO2 that is produced by burning one liter of oil can be sequestered by less than one liter of olivine. The reaction is exothermic but slow. To recover the heat produced by the reaction to produce electricity, a large volume of olivine must be thermally well-isolated. The end-products of the reaction are silicon dioxide, magnesium carbonate, and small amounts of iron oxide.
Olivine is used as a substitute for dolomite in steel works. [ citation needed ]Olivine is also used to tap blast furnaces in the steel industry, acting as a plug, removed in each steel run.
The aluminium foundry industry uses olivine sand to cast objects in aluminium. Olivine sand requires less water than silica sands while still holding the mold together during handling and pouring of the metal. Less water means less gas (steam) to vent from the mold as metal is poured into the mold.
In Finland, olivine is marketed as an ideal rock for sauna stoves because of its comparatively high density and resistance to weathering under repeated heating and cooling.
The pyroxenes (commonly abbreviated to Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula XY(Si,Al)2O6 where X represents calcium, sodium, iron (II) or magnesium and more rarely zinc, manganese or lithium and Y represents ions of smaller size, such as chromium, aluminium, iron (III), magnesium, cobalt, manganese, scandium, titanium, vanadium or even iron (II). Although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes. They share a common structure consisting of single chains of silica tetrahedra. Pyroxenes that crystallize in the monoclinic system are known as clinopyroxenes and those that cystallize in the orthorhombic system are known as orthopyroxenes.
Periclase is a magnesium mineral that occurs naturally in contact metamorphic rocks and is a major component of most basic refractory bricks. It is a cubic form of magnesium oxide (MgO). In nature it usually forms a solid solution with wüstite (FeO) and is then referred to as ferropericlase or magnesiowüstite.
Magnesite is a mineral with the chemical formula MgCO3 (magnesium carbonate). Iron, manganese, cobalt and nickel may occur as admixtures, but only in small amounts.
Peridotite is a dense, coarse-grained igneous rock consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica (SiO4−
4). It is high in magnesium (Mg2+), reflecting the high proportions of magnesium-rich olivine, with appreciable iron. Peridotite is derived from the Earth's mantle, either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle. The compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole.
Glaucophane is the name of a mineral and a mineral group belonging to the sodic amphibole supergroup of the double chain inosilicates, with the chemical formula ☐Na2(Mg3Al2)Si8O22(OH)2.
Fayalite (Fe2SiO4; commonly abbreviated to Fa), also called iron chrysolite, 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.
Cummingtonite is a metamorphic amphibole with the chemical composition (Mg,Fe2+)2(Mg,Fe2+)5Si8O22(OH)2, magnesium iron silicate hydroxide.
Serpentinite is a rock composed of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake. Minerals in this group, which are rich in magnesium and water, light to dark green, greasy looking and slippery feeling, are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle. The mineral alteration is particularly important at the sea floor at tectonic plate boundaries.
Melilite refers to a mineral of the melilite group. Minerals of the group are solid solutions of several endmembers, the most important of which are gehlenite and åkermanite. A generalized formula for common melilite is (Ca,Na)2(Al,Mg,Fe2+)[(Al,Si)SiO7]. Discovered in 1793 near Rome, it has a yellowish, greenish-brown color. The name derives from the Greek words meli (μέλι) "honey" and lithos (λίθους) "stone".
The transition zone is part of the Earth’s mantle, and is located between the lower mantle and the upper mantle, between a depth of 410 and 660 km. The Earth’s mantle, including the transition zone, consists primarily of peridotite, an ultramafic igneous rock.
Alfred Edward "Ted" Ringwood FRS FAA was an Australian experimental geophysicist and geochemist, and the 1988 recipient of the Wollaston Medal.
In geology, a redox buffer is an assemblage of minerals or compounds that constrains oxygen fugacity as a function of temperature. Knowledge of the redox conditions (or equivalently, oxygen fugacities) at which a rock forms and evolves can be important for interpreting the rock history. Iron, sulfur, and manganese are three of the relatively abundant elements in the Earth's crust that occur in more than one oxidation state. For instance, iron, the fourth most abundant element in the crust, exists as native iron, ferrous iron (Fe2+), and ferric iron (Fe3+). The redox state of a rock affects the relative proportions of the oxidation states of these elements and hence may determine both the minerals present and their compositions. If a rock contains pure minerals that constitute a redox buffer, then the oxygen fugacity of equilibration is defined by one of the curves in the accompanying fugacity-temperature diagram.
Wadsleyite is a high-pressure phase of polymorphous Mg2SiO4. An orthorhombic mineral with the formula β-Mg2SiO4, it was first found in nature in the Peace River meteorite from Alberta, Canada. It is formed by a phase transformation from forsterite (α-Mg2SiO4) under increasing pressure and eventually transforms into spinel-structured ringwoodite (γ-Mg2SiO4) as pressure increases further. The structure can take up a limited amount of other bivalent cations instead of magnesium, but contrary to the α and γ structures, a β structure with the sum formula Fe2SiO4 is not thermodynamically stable. Its cell parameters are approximately a = 5.7 Å, b = 11.7 Å and c = 8.24 Å.
Ringwoodite is a high-pressure phase of Mg2SiO4 formed at high temperatures and pressures of the Earth's mantle between 525 and 660 km (326 and 410 mi) depth. It is polymorphous with the olivine phase forsterite (a magnesium iron silicate).
Tenham meteorites are the fragments of a larger meteorite that fell in 1879 in a remote area of Australia near the Tenham station, South Gregory, in western Queensland. Although the fall was seen by a number of people its exact date has not been established. Bright meteors were seen to be moving roughly from west to east. Stones were subsequently recovered from over a large area, about 20 kilometres (12 mi) long by 5 kilometres (3.1 mi) wide.
Silicate perovskite is either (Mg,Fe)SiO3 (the magnesian end-member is called bridgmanite) or CaSiO3 (calcium silicate) when arranged in a perovskite structure. Silicate perovskites are not stable at Earth's surface, and are mainly found in the lower part of Earth's mantle, between about 670 and 2,700 km (420 and 1,680 mi) depth. They are thought to form the main mineral phases, together with ferropericlase.
Specific Gravity 3.5–4.5
The specific gravity is approximately 3.2 when pure rises with increasing iron content.
G = 3.22 to 4.39. Specific gravity increases and hardness decreases with increasing Fe.
Specific Gravity: 3.2 (Mg-rich variety) to 4.3 (Iron-rich variety) (average weight)
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