Chondrodite
Encyclopedia
Chondrodite is a nesosilicate mineral
with formula (Mg,Fe)5(SiO4)2(F,OH,O)2. Although it is a fairly rare mineral, it is the most frequently encountered member of the humite group
of minerals. It is formed in hydrothermal deposits from locally metamorphosed dolomite
. It is also found associated with skarn
and serpentinite
.
It was discovered in 1817 on Mt. Somma, part of the Vesuvius complex in Italy
, and named from the Greek for "granule", which is a common habit for this mineral.
, molar mass 351.6 g. There is usually some OH in the F sites, however, and Fe and Ti can substitute for Mg, so the formula for the naturally occurring mineral is better written (Mg,Fe,Ti)5(SiO4)2(F,OH,O)2.
Unit Cell Parameters:
Synthetic F end member a=7.80 Å, b=4.75 Å, c=10.27 Å, beta=109.2o.
Synthetic OH end member a=7.914 Å, b=4.752 Å, c=10.350 Å, beta=108.71o.
Natural chondrodite has a=7.867 to 7.905 Å, b=4.727 to 4.730 Å, c=10.255 to 10.318 Å, beta=109.0o to 109.33o.
Z=2.
Chondrodite is yellow, orange, red or brown, or rarely colorless, but zoning of different color intensity is common, and intergrown plates of chondrodite, humite, clinohumite, forsterite
and monticellite
have been reported.
contact zones between carbonate rock
s and acidic or alkaline intrusions where fluorine
has been introduced by metasomatic processes. It is formed by the hydration of olivine
, (Mg,Fe2+)2SiO4, and is stable over a range of temperatures and pressures that include those existing in a portion of the uppermost mantle
.
Titanian chondrodite has been found as inclusions in olivine in serpentinite
in West Greenland, where it is associated with clinohumite, olivine, magnesite
, magnetite
and Ni-Co-Pb sulfides in a matrix of antigorite.
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
with formula (Mg,Fe)5(SiO4)2(F,OH,O)2. Although it is a fairly rare mineral, it is the most frequently encountered member of the humite group
Humite (mineral group)
The humite group is a group of nesosilicates with the general formula Anm2.When A is predominantly magnesium we have the humite subgroup:*norbergite, Mg32*chondrodite, 522*humite, 732...
of minerals. It is formed in hydrothermal deposits from locally metamorphosed dolomite
Dolomite
Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
. It is also found associated with skarn
Skarn
Skarn is an old Swedish mining term originally used to describe a type of silicate gangue, or waste rock, associated with iron-ore bearing sulfide deposits apparently replacing Archean age limestones in Sweden's Persberg mining district. In modern usage the term "skarn" has been expanded to refer...
and serpentinite
Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...
.
It was discovered in 1817 on Mt. Somma, part of the Vesuvius complex in Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, and named from the Greek for "granule", which is a common habit for this mineral.
Formula
Mg5(SiO4)2F2 is the end member formula as given by the International Mineralogical AssociationInternational Mineralogical Association
The International Mineralogical Association is an international group of 38 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 4000 plus known mineral species...
, molar mass 351.6 g. There is usually some OH in the F sites, however, and Fe and Ti can substitute for Mg, so the formula for the naturally occurring mineral is better written (Mg,Fe,Ti)5(SiO4)2(F,OH,O)2.
Structure
The chondrodite structure is based on a slightly distorted hexagonal close packed array of anions O, OH and F with metal ions in the octahedral sites resulting in zigzag chains of M(O,OH,F)6 octahedra. Chains are staggered so that none of the independent tetrahedral sites occupied by Si has OH or F corners. Half of the octahedral sites are filled by divalent cations, principally Mg, and one tenth of the tetrahedral sites are filled by Si. There are three distinct octahedra in the array: Fe is ordered in the M1 sites but not in the larger M2 and smaller M3 sites. Ti is ordered in the M3 positions, which are the smallest, but Ti concentration appears never to exceed 0.5 atoms Ti per formula unit in natural specimens. In the humite series Mg2+ is replaced by Fe2+, Mn2+, Ca2+ and Zn2+ in that order of abundance, though Mg2+ always predominates.Unit cell
Space Group: P21/bUnit Cell Parameters:
Synthetic F end member a=7.80 Å, b=4.75 Å, c=10.27 Å, beta=109.2o.
Synthetic OH end member a=7.914 Å, b=4.752 Å, c=10.350 Å, beta=108.71o.
Natural chondrodite has a=7.867 to 7.905 Å, b=4.727 to 4.730 Å, c=10.255 to 10.318 Å, beta=109.0o to 109.33o.
Z=2.
Color
Forsterite
Forsterite is the magnesium rich end-member of the olivine solid solution series. Forsterite crystallizes in the orthorhombic system with cell parameters a 4.75 Å , b 10.20 Å and c 5.98 Å .Forsterite is associated with igneous and metamorphic rocks and has also been found in meteorites...
and monticellite
Monticellite
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.%...
have been reported.
Optical properties
Chondrodite is biaxial(+), with refractive indices variously reported as nα = 1.592 - 1.643, nβ = 1.602 - 1.655, nγ = 1.619 - 1.675, birefringence = 0.025 - 0.037, and 2V measured as 64° to 90°, calculated: 76° to 78°. Refractive indices tend to increase from norbergite to clinohumite in the humite group. They also increase with Fe2+ and Ti4+ and with (OH)- substituting for F-. Dispersion: r > v.Environment
Chondrite is found largely in metamorphicMetamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
contact zones between carbonate rock
Carbonate rock
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 and dolostone, which is composed of the mineral dolomite .Calcite can be either dissolved by groundwater or precipitated by...
s and acidic or alkaline intrusions where fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
has been introduced by metasomatic processes. It is formed by the hydration of olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
, (Mg,Fe2+)2SiO4, and is stable over a range of temperatures and pressures that include those existing in a portion of the uppermost mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
.
Titanian chondrodite has been found as inclusions in olivine in serpentinite
Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...
in West Greenland, where it is associated with clinohumite, olivine, magnesite
Magnesite
Magnesite is magnesium carbonate, MgCO3. Iron substitutes for magnesium with a complete solution series with siderite, FeCO3. Calcium, manganese, cobalt, and nickel may also occur in small amounts...
, magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...
and Ni-Co-Pb sulfides in a matrix of antigorite.
See also
- JerrygibbsiteJerrygibbsiteJerrygibbsite is a rare silicate mineral with chemical formula: 942. Jerrygibbsite was originally discovered by Pete J. Dunn in 1984, who named it after mineralogist Gerald V. Gibbs. It has only been reported from the type locality of Franklin Furnace, New Jersey, United States, and in Namibia's...
- ClinohumiteClinohumiteClinohumite is an uncommon member of the humite group, a magnesium silicate according to the chemical formula 942. Most commonly found as tiny indistinct grains, large euhedral clinohumite crystals are sought by collectors and occasionally fashioned into bright, yellow-orange gemstones...
- AlleghanyiteAlleghanyiteAlleghanyite is a moderately rare humite mineral with formula Mn522, belonging to the nesosilicates class. In general its occurrences are related with metamorphic manganese deposits. The mineral is named after Alleghany County, North Carolina, USA....
- HumiteHumiteHumite is a mineral found in the volcanically ejected masses of Vesuvius. It was first described in 1813 and named for Abraham Hume .-See also:* Jerrygibbsite* Chondrodite* Clinohumite* Alleghanyite...
- Classification of minerals
- List of minerals