Gedrite

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Gedrite
Gedrite-Magnetite-448448.jpg
Gedrite on a feldspar matrix
General
CategoryInosilicate, ferromagnesian amphibole group
Formula
(repeating unit)
Mg2(Mg3Al2)(Si6Al2)O22(OH)2
IMA symbol Ged [1]
Strunz classification 9.DD.05
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pnma
Unit cell a = 18.59, b = 17.89
c = 5.3 [Å]; Z = 4
Identification
ColorWhite, gray, brown, green, black
Crystal habit Bladed and prismatic crystals; fibrous and sheath like aggregates.
Twinning contact twinning
Cleavage 56 and 126° – good; {210} perfect
Fracture Splintery
Mohs scale hardness5.5–6
Luster Vitreous to silky
Diaphaneity Translucent, will transmit light on thin edges.
Specific gravity 3.18–3.33
Optical propertiesBiaxial (+)
Refractive index nα = 1.671 nβ = 1.681 nγ = 1.690
Birefringence δ = 0.019
Pleochroism Weak to moderate
2V angle Measured: 75°
References [2] [3] [4] [5]

Gedrite is a crystal belonging to the orthorhombic ferromagnesian subgroup of the amphibole supergroup of the double chain inosilicate minerals with the ideal chemical formula Mg2(Mg3Al2)(Si6Al2)O22(OH)2.

Gedrite is the magnesium (Mg) rich endmember of a solid solution series, with divalent magnesium cations readily replaced with ferrous iron (Fe), leading to the iron rich endmember 'ferrogedrite', with the formula: Fe2+2(Fe2+3Al2)(Si6Al2)O22(OH)2. However, pure endmembers are very rare, with often either one of the mentioned cations dominating the composition. Thus, the formula can be written in such a way to express common intermediary gedrite samples: (Mg,Fe)2+2(Mg,Fe)2+3Al2(Al2Si6O22)(OH)2.

Divalent manganese (Mn) may substitute for some of the magnesium. Trivalent or ferric iron, or titanium 4+ may replace some of the aluminum (Al). Fluorine and chlorine are common substitutes for the hydroxyl (OH) in amphoboles. Other chemical impurities may include calcium, sodium, and potassium.

Gedrite also forms a series with another ferromagnesian amphibole, anthophyllite.

Gedrite occurs in contact and medium to high grade metamorphic rocks in association with garnet, cordierite, anthophyllite, cummingtonite, sapphirine, sillimanite, kyanite, quartz, staurolite and biotite. [2]

Gedrite was first described for an occurrence in Gèdre, Hautes-Pyrenees, France in 1836. [3]

Related Research Articles

<span class="mw-page-title-main">Hornblende</span> Complex inosilicate series of minerals

Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks.

<span class="mw-page-title-main">Amphibole</span> Group of inosilicate minerals

Amphibole is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain SiO
4
tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is Amp. Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The International Mineralogical Association currently classifies amphiboles as a mineral supergroup, within which are two groups and several subgroups.

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

Actinolite is an amphibole silicate mineral with the chemical formula Ca2(Mg4.5–2.5Fe2+0.5–2.5)Si8O22(OH)2.

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

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.

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

Fayalite 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 with cell parameters a 4.82 Å, b 10.48 Å and c 6.09 Å.

<span class="mw-page-title-main">Cummingtonite</span> Silicate mineral

Cummingtonite is a metamorphic amphibole with the chemical composition (Mg,Fe2+
)
2
(Mg,Fe2+
)
5
Si
8
O
22
(OH)
2
, magnesium iron silicate hydroxide.

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

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.

<span class="mw-page-title-main">Melilite</span> Sorosilicate mineral

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 name refers to a group of minerals (melilite group) with chemically similar composition, nearly always minerals in åkermanite-gehlenite series.

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

Galaxite, also known as 'mangan-spinel' is an isometric mineral belonging to the spinel group of oxides with the ideal chemical formula Mn2+Al2O4.

<span class="mw-page-title-main">Nontronite</span> Dioctahedral (Fe3+) smectite, phyllosilicate mineral

Nontronite is the iron(III) rich member of the smectite group of clay minerals. Nontronites typically have a chemical composition consisting of more than ~30% Fe2O3 and less than ~12% Al2O3 (ignited basis). Nontronite has very few economic deposits like montmorillonite. Like montmorillonite, nontronite can have variable amounts of adsorbed water associated with the interlayer surfaces and the exchange cations.

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

Scorzalite ((Fe2+,Mg)Al2(OH,PO4)2) is a dark blue phosphate mineral containing iron, magnesium, and aluminium phosphate. Scorzalite forms one endmember of a solid solution series with the lighter, more magnesium-rich lazulite.

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

The endmember hornblende tschermakite (☐Ca2(Mg3Al2)(Si6Al2)O22(OH)2) is a calcium rich monoclinic amphibole mineral. It is frequently synthesized along with its ternary solid solution series members tremolite and cummingtonite so that the thermodynamic properties of its assemblage can be applied to solving other solid solution series from a variety of amphibole minerals.

<span class="mw-page-title-main">Kaersutite</span> Calcic titanium bearing amphibole mineral

Kaersutite is a dark brown to black double chain calcic titanium bearing amphibole mineral with formula: NaCa2(Mg3Ti4+Al)(Si6Al2)O22(O)2.

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

Chesterite is a rare silicate mineral that can be compared to amphiboles, micas, and jimthompsonite. Its chemical formula is (Mg,Fe)
17
Si
20
O
54
(OH)
6
. Chesterite is named after Chester, Vermont, where it was first described in 1977. The specific geologic setting within its origin is the Carleton talc quarry in Chester, Vermont.

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">Magnesiohastingsite</span>

Magnesiohastingsite is a calcium-containing amphibole and a member of the hornblende group. It is an inosilicate (chain silicate) with the formula NaCa2(Mg4Fe3+)(Si6Al2)O22(OH)2 and molar mass 864.69 g. In synthetic magnesiohastingsite it appears that iron occurs both as ferrous iron Fe2+ and as ferric iron Fe3+, but the ideal formula features only ferric iron. It was named in 1928 by Marland P. Billings. The name is for its relationship to hastingsite and its magnesium content. Hastingsite was named for the locality in Dungannon Township, Hastings County, Ontario, Canada.

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

Jimthompsonite is a magnesium iron silicate mineral with chemical formula (Mg,Fe2+)5Si6O16(OH)2. It is a triple chain silicate (or inosilicate) along with clinojimthompsonite and chesterite. They were described in 1977 by Burham and Veblen. They attracted great mineralogical attention because they were the first examples of new chain silicate structures among a large group known as biopyriboles whose name is derived from the words biotite, pyroxene, and amphiboles.

Amakinite (IMA symbol: Amk) is a semi transparent yellow-green hydroxide mineral belonging to the brucite group that was discovered in 1962. Its chemical formula is written as (Fe2+,Mg)(OH)2. It usually occurs in the form of splotchy, anhedral crystals forming within a group or structure in other minerals or rocks, such as kimberlite (occurring in diamond-rich eruptive pipe). Its composition is as follows:

<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.

Magnesiocummingtonite is the magnesium rich endmember of the cummingtonite-grunerite series of the amphibole group of minerals, with the following composition: (Mg)7Si8O22(OH)2.

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 http://www.handbookofmineralogy.org/pdfs/gedrite.pdf Handbook of Mineralogy
  3. 1 2 http://webmineral.com/data/Gedrite.shtml Webmineral
  4. http://www.mindat.org/min-1665.html Mindat
  5. IMA Master List