Chondrodite

Last updated
Chondrodite
Chondrodite-225224.jpg
General
Category Nesosilicates
Formula
(repeating unit)
Mg
5
(SiO
4
)
2
F
2
IMA symbol Chn [1]
Strunz classification 9.AF.45 (10th edition)
8/B.04-20 (8th edition)
Dana classification 52.3.2b.2
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/a
Identification
Formula mass 351.6 g/mol
ColorYellow, orange, red or brown, rarely colorless
Crystal habit Typically anhedral masses or grains, or as plates flattened on {010}, {001} or {100}. [2]
Twinning Simple or multiple twinning common on {001}, also reported on {105} and {305}. [2]
Cleavage Poor to good on (001)
Fracture Conchoidal to uneven
Tenacity Brittle
Mohs scale hardness6 to 6.5
Luster Vitreous to greasy
Streak Grey or yellow
Diaphaneity Translucent
Specific gravity 3.1 to 3.26
Optical propertiesBiaxial(+)
Refractive index nα = 1.592 – 1.643, nβ = 1.602 – 1.655, nγ = 1.619 – 1.675,
Birefringence 0.027 – 0.032
Pleochroism X golden yellow to orange, Y and Z light yellow to almost colorless [3]
Solubility Soluble in HCl and H2SO4
Other characteristicsSome specimens fluoresce orange yellow under shortwave and orange under longwave UV. Not radioactive.
References [4] [5] [6] [7] [8]

Chondrodite is a nesosilicate mineral with formula (Mg,Fe)
5
(SiO
4
)
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 at Pargas in Finland, and named from the Greek for "granule", which is a common habit for this mineral. [9]

Contents

Formula

Mg
5
(SiO
4
)
2
F
2
is the end member formula as given by the International Mineralogical Association, [10] 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
(SiO
4
)
2
(F,OH,O)
2
. [5]

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. [2] 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. [11] 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. [12] In the humite series Mg2+ is replaced by Fe2+, Mn2+, Ca2+ and Zn2+ in that order of abundance, though Mg2+ always predominates. [2]

Unit cell

Space group: P21/b 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.

Color

Chondrodite with magnetite, Tilly Foster mine, Brewster, New York, US Chondrodite with magnetite and silicate Basic magnesium fluosilicate Tilly Foster Mine, Brewster, Putnam County, New York 2659.jpg
Chondrodite with magnetite, Tilly Foster mine, Brewster, New York, US

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. [2]

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. [2] Dispersion: r > v.

Environment

Chondrodite is found largely in metamorphic contact zones between carbonate rocks 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. [13]

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. [14] [15]

See also

Related Research Articles

<span class="mw-page-title-main">Pyroxene</span> Group of inosilicate minerals with single chains of silica tetrahedra

The pyroxenes 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 (Ca), sodium (Na), iron or magnesium (Mg) and more rarely zinc, manganese or lithium, and Y represents ions of smaller size, such as chromium (Cr), aluminium (Al), magnesium (Mg), cobalt (Co), manganese (Mn), scandium (Sc), titanium (Ti), vanadium (V) or even iron. 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 crystallize in the orthorhombic system are known as orthopyroxenes.

<span class="mw-page-title-main">Sekaninaite</span> Mg, Fe, Al cyclosilicate mineral

Sekaninaite ((Fe+2,Mg)2Al4Si5O18) is a silicate mineral, the iron-rich analogue of cordierite.

<span class="mw-page-title-main">Armalcolite</span> Oxide mineral

Armalcolite is a titanium-rich mineral with the chemical formula (Mg,Fe2+)Ti2O5. It was first found at Tranquility Base on the Moon in 1969 during the Apollo 11 mission, and is named for Armstrong, Aldrin and Collins, the three Apollo 11 astronauts. Together with tranquillityite and pyroxferroite, it is one of three new minerals that were discovered on the Moon. Armalcolite was later identified at various locations on Earth and has been synthesized in the laboratory. (Tranquillityite and pyroxferroite were also later found at various locations on Earth). The synthesis requires low pressures, high temperatures and rapid quenching from about 1,000 °C to the ambient temperature. Armalcolite breaks down to a mixture of magnesium-rich ilmenite and rutile at temperatures below 1,000 °C, but the conversion slows down with cooling. Because of this quenching requirement, armalcolite is relatively rare and is usually found in association with ilmenite and rutile, among other minerals.

<span class="mw-page-title-main">Forsterite</span> Magnesium end-member of olivine, a nesosilicate mineral

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).

<span class="mw-page-title-main">Silicate mineral</span> Rock-forming minerals with predominantly silicate anions

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.

<span class="mw-page-title-main">Clinohumite</span> Nesosilicate mineral

Clinohumite is an uncommon member of the humite group, a magnesium silicate according to the chemical formula (Mg, Fe)9(SiO4)4(F,OH)2. The formula can be thought of as four olivine (Mg2SiO4), plus one brucite (Mg(OH)2). Indeed, the mineral is essentially a hydrated olivine and occurs in altered ultramafic rocks and carbonatites. Most commonly found as tiny indistinct grains, large euhedral clinohumite crystals are sought by collectors and occasionally fashioned into bright, yellow-orange gemstones. Only two sources of gem-quality material are known: the Pamir Mountains of Tajikistan, and the Taymyr region of northern Siberia. It is one of two humite group minerals that have been cut into gems, the other being the much more common chondrodite.

<span class="mw-page-title-main">Ceylonite</span>

Ceylonite and pleonaste or pleonast are dingy blue or grey to black varieties of spinel. Ceylonite, named for the island of Ceylon, is a ferroan spinel with Mg:Fe from 3:1 and 1:1, and little or no ferric iron. Pleonaste is named from the Greek for 'abundant,' for its many crystal forms, and is distinguished chemically by low Mg:Fe ratios of approximately 1:3. It is sometimes used as a gemstone.

An endmember in mineralogy is a mineral that is at the extreme end of a mineral series in terms of purity of its chemical composition. Minerals often can be described as solid solutions with varying compositions of some chemical elements, rather than as substances with an exact chemical formula. There may be two or more endmembers in a group or series of minerals.

<span class="mw-page-title-main">Wadsleyite</span> Mineral thought to be abundant in the Earths mantle

Wadsleyite is an orthorhombic mineral with the formula β-(Mg,Fe)2SiO4. It was first found in nature in the Peace River meteorite from Alberta, Canada. It is formed by a phase transformation from olivine (α-(Mg,Fe)2SiO4) under increasing pressure and eventually transforms into spinel-structured ringwoodite (γ-(Mg,Fe)2SiO4) 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 = 11.71 Å and c = 8.24 Å.

<span class="mw-page-title-main">Julgoldite</span>

Julgoldite is a member of the pumpellyite mineral series, a series of minerals characterized by the chemical bonding of silica tetrahedra with alkali and transition metal cations. Julgoldites, along with more common minerals like epidote and vesuvianite, belong to the subclass of sorosilicates, the rock-forming minerals that contain SiO4 tetrahedra that share a common oxygen to form Si2O7 ions with a charge of 6− (Deer et al., 1996). Julgoldite has been recognized for its importance in low grade metamorphism, forming under shear stress accompanied by relatively low temperatures (Coombs, 1953). Julgoldite was named in honor of Professor Julian Royce Goldsmith (1918–1999) of the University of Chicago.

Zussmanite is a hydrated iron-rich silicate mineral with the chemical formula K(Fe2+,Mg,Mn)13[AlSi17O42](OH)14. It occurs as pale green crystals with perfect cleavage.

<span class="mw-page-title-main">Alleghanyite</span> Nesosilicate mineral

Alleghanyite is a moderately rare humite mineral with formula Mn5(SiO4)2(OH)2, belonging to the nesosilicates class. In general its occurrences are related with metamorphic (metamorphosed) manganese deposits. The mineral is named after Alleghany County, North Carolina, US.

<span class="mw-page-title-main">Fluor-liddicoatite</span>

Fluor-liddicoatite is a rare member of the tourmaline group of minerals, elbaite subgroup, and the theoretical calcium endmember of the elbaite-fluor-liddicoatite series; the pure end-member has not yet been found in nature. Fluor-liddicoatite is indistinguishable from elbaite by X-ray diffraction techniques. It forms a series with elbaite and probably also with olenite. Liddiocoatite is currently a non-approved mineral name, but Aurisicchio et al. (1999) and Breaks et al. (2008) found OH-dominant species. Formulae are

The humite group is a group of nesosilicates with the general formula An(SiO4)m(F,OH)2.

This list gives an overview of the classification of minerals (silicates) and includes mostly International Mineralogical Association (IMA) recognized minerals and its groupings. This list complements the List of minerals recognized by the International Mineralogical Association series of articles and List of minerals. Rocks, ores, mineral mixtures, non-IMA approved minerals and non-named minerals are mostly excluded.

<span class="mw-page-title-main">Pimelite</span> Nickel-rich smectite deprecated as mineral species in 2006

Pimelite was discredited as a mineral species by the International Mineralogical Association (IMA) in 2006, in an article which suggests that "pimelite" specimens are probably willemseite, or kerolite. This was a mass discreditation, and not based on any re-examination of the type material. Nevertheless, a considerable number of papers have been written, verifying that pimelite is a nickel-dominant smectite. It is always possible to redefine a mineral wrongly discredited.

<span class="mw-page-title-main">Satterlyite</span>

Satterlyite is a hydroxyl bearing iron phosphate mineral. The mineral can be found in phosphatic shales and was first discovered in the Big Fish River area in Yukon Territory, Canada.

<span class="mw-page-title-main">Ferrogedrite</span> Amphibole, double chain inosilicate mineral

Ferrogedrite is an amphibole mineral with the complex chemical formula of ☐Fe2+2(Fe2+3Al2)(Si6Al2)O22(OH)2. It is sodium and calcium poor, making it part of the magnesium-iron-manganese-lithium amphibole subgroup. Defined as less than 1.00 apfu (atoms per formula unit) of Na + Ca and consisting of greater than 1.00 apfu of (Mg, Fe2+, Mn2+, Li) separating it from the calcic-sodic amphiboles. It is related to anthophyllite amphibole and gedrite through coupled substitution of (Al, Fe3+) for (Mg, Fe2+, Mn) and Al for Si. and determined by the content of silicon in the standard cell.

<span class="mw-page-title-main">Coupled substitution</span> Geological process by which two elements simultaneously substitute into a crystal

Coupled substitution is the geological process by which two elements simultaneous substitute into a crystal in order to maintain overall electrical neutrality and keep the charge constant. In forming a solid solution series, ionic size is more important than ionic charge, as this can be compensated for elsewhere in the structure.

Antigorite Monoclinic mineral

Antigorite is a lamellated, monoclinic mineral in the phyllosilicate serpentine subgroup with the ideal chemical formula of (Mg,Fe2+)3Si2O5(OH)4. It is the high-pressure polymorph of serpentine and is commonly found in metamorphosed serpentinites. Antigorite, and its serpentine polymorphs, play an important role in subduction zone dynamics due to their relative weakness and high weight percent of water (up to 13 weight % H2O). It is named after its type locality, the Geisspfad serpentinite, Valle Antigorio in the border region of Italy/Switzerland and is commonly used as a gemstone in jewelry and carvings.

References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. 1 2 3 4 5 6 Phillips, W R and Griffen, D T (1981) Optical Mineralogy, pages 142 to 144
  3. European Journal of Mineralogy (2002) 14: 1027-1032
  4. "Chondrodite". Mineralienatlas.
  5. 1 2 Gaines et al (1997) Dana's New Mineralogy Eighth Edition, Wiley
  6. "Chondrodite". Mindat.
  7. "Chondrodite Mineral Data". WebMineral.
  8. "Chondrodite" (PDF). RRUFF. Retrieved 14 June 2024.
  9. Hintze, C. (31 December 1897). "Humitgruppe". Silicate und Titanate: 370–406. doi:10.1515/9783112361047-011. ISBN   9783112361047. The usually granular occurrence in the limestone of Pargas in Finland was described by D'OHSSON (Vet. Akad. Handl. Stockh. 1817, 206) after χονδρος "granule" as chondrodite
  10. "IMA Mineral List with Database of Mineral Properties".
  11. American Mineralogist (1970): 55: 1182-1194
  12. American Mineralogist (1979) 64:1027
  13. Physics and Chemistry of Minerals (1999) 26: 297-303
  14. "Petrogenesis of Ultramafic Metamorphic Rocks from the 3800 Ma Isua Supracrustal Belt, West Greenland". petrology.oxfordjournals.org. Archived from the original on 20 September 2013. Retrieved 27 January 2022.
  15. Friend, C.R.L.; Nutman, A.P. (2011). "Dunites from Isua, Greenland: A ca. 3720 Ma window into subcrustal metasomatism of depleted mantle". Geology. 39 (7): 663–666. Bibcode:2011Geo....39..663F. doi:10.1130/G31904.1.