Gehlenite, (Ca
2Al
lSiO7, is a
sorosilicate
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.
In mineralogy, silica (silicon dioxide, ) is usually consid ...
, Al-rich endmember of the
melilite complete
solid solution
A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wor ...
series with
akermanite.
[Deer et al., 1993][Gehlenite: Gehlenite mineral information and data]
/ref>
The type locality
Type locality may refer to:
* Type locality (biology)
* Type locality (geology)
See also
* Local (disambiguation)
* Locality (disambiguation)
{{disambiguation ...
is in the Monzoni Mountains, Fassa Valley in Trentino
Trentino ( lld, Trentin), officially the Autonomous Province of Trento, is an autonomous province of Italy, in the country's far north. The Trentino and South Tyrol constitute the region of Trentino-Alto Adige/Südtirol, an autonomous regio ...
in Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
,[Dana et al. 1997]
Geological occurrence
Gehlenite is found in carbonaceous chondrites from which it condensed as a refractory mineral in the hotter stages ( FU Ori) of the presolar nebula
A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...
,[Grossman L (1972) Condensation in the primitive solar nebula, Geochemica et Cosmochemica Acta, 36, 597-619] and was subsequently consumed in processes which created enstatite
Enstatite is a mineral; the magnesium endmember of the pyroxene silicate mineral series enstatite (MgSiO3) – ferrosilite (FeSiO3). The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous a ...
and other more abundant minerals making it a remnant mineral from the early solar nebula (along with corundum
Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the ...
and spinel
Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals.
Properties
...
). Its occurrence in the early condensation phase of the solar nebula was predicted by Harry Lord in the 1950s, but studies of carbonaceous chondrites did not support this claim until the Allende
Salvador Guillermo Allende Gossens (, , ; 26 June 1908 – 11 September 1973) was a Chilean physician and socialist politician who served as the 28th president of Chile from 3 November 1970 until his death on 11 September 1973. He was the fi ...
meteorite was discovered in 1969. It is also found in diorite
Diorite ( ) is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-sil ...
intruded carbonate rocks
Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3), and dolomite rock (also known as doloston ...
,[Carmichael ISE, Turner FJ, Verhoogen J (1974) Igneous Petrology, 37] and to a far lesser extent in uncompahgrites,[Le Maitre RW (2002), Igneous Rocks, 11, 153] melilitites,[Nixon PH (1987) Mantle Xenoliths, 102-103, 336, 450-451] lamprophyres and possibly kimberlite
Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known to be the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond called the Star of S ...
pipes.[Skinner EMW, Mahotkin IL, Grutter HS (1999) Melilite in Kimberlites, Proceedings of the International Kimberlite Conference, 7, 788-794]
Gehlenite has also been found on the comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or Coma (cometary), coma, and sometimes also a Comet ta ...
81P/Wild
Comet 81P/Wild, also known as Wild 2 (pronounced "vilt two") ( ), is a comet named after Swiss astronomer Paul Wild, who discovered it on January 6, 1978, using a 40-cm Schmidt telescope at Zimmerwald, Switzerland.
For most of its 4.5 billio ...
.Mindat page for Comet Wild 2 (Comet 81P)
/ref>
Crystallography, composition and physical properties
Gehlenite is one of five, isostructural tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squ ...
minerals in the melilite group. The tetrahedral linkage within the structure is similar to that of an aluminosilicate
Aluminosilicate minerals ( IMA symbol: Als) are minerals composed of aluminium, silicon, and oxygen, plus countercations. They are a major component of kaolin and other clay minerals.
Andalusite, kyanite, and sillimanite are naturally ...
framework structure[Louisnathan S (1969), Refinement of the crystal structure of gehlenite, Canadian Mineralogist, 10, 822-837] and was once considered a feldspathoid
The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. They occur in rare and unusual types of igneous rocks, and are usually not found in rocks containing pri ...
-like mineral[Best MG (2003), Igneous and Metamorphic Petrology (2nd Ed), 398, 693, 702-703] due to silica undersaturation.
Gehlenite has a Mohs hardness
The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material.
The scale was introduced in 1812 by the ...
of 5-6, a vitreous to greasy lustre, distinct to good cleavage and is yellow brown, greenish grey or colourless. Its streak is white or grey-white.uniaxial In crystal optics, the index ellipsoid (also known as the ''optical indicatrix'' or sometimes as the ''dielectric ellipsoid'') is a geometric construction which concisely represents the refractive indices and associated polari ...
(-), has an anomalous nonzero 2V angle A conoscopic interference pattern or interference figure is a pattern of birefringent colours crossed by dark bands (or ''isogyres''), which can be produced using a geological petrographic microscope for the purposes of mineral identification and in ...
and has a characteristic 'ultrablue' birefringence
Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefrin ...
.
References
{{reflist, 2
Sorosilicates
Aluminium minerals
Calcium minerals
Tetragonal minerals
Minerals in space group 113