Grossular

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Grossular
Grossular-ww51a.jpg
Grossular dodecahedron, 7 mm across, from Coahuila, Mexico
General
Category Nesosilicate
Formula
(repeating unit)		Ca3Al2(SiO4)3
IMA symbol Grs [1]
Strunz classification 9.AD.25
Crystal system Cubic [2]
Crystal class Hexoctahedral (m3m)
H-M Symbol: (4/m 3 2/m)
Space group Ia3d
Identification
Colorlight to dark green, light to dark yellow to reddish brown, brown, orange, red, yellow, green, white, occasionally translucent to opaque pink. It is also but rarely found in colorless form [2]
Cleavage none
Fracture conchoidal to uneven [2]
Mohs scale hardness6.5 to 7 [2]
Luster greasy to vitreous [2]
Streak Brown
Specific gravity 3.61 (+.15/−.04)
Polish lustervitreous [2]
Optical propertiesSingle refractive, often anomalous double refractive [2]
Refractive index 1.740 (+.12/−.04) [2]
Birefringence none
Pleochroism none
Dispersion .028
Ultraviolet fluorescence near colorless to light green – inert to weak orange in longwave and weak yellow-orange in shortwave; yellow – inert to weak orange in longwave and shortwave [2]
Absorption spectra Hessonite sometimes shows bands at 407 and 430 nm
Major varieties
Hessonite yellow-red to reddish-orange
Tsavorite intense green to yellowish green
Leuco-garnet transparent and colorless [3]
Rosolite translucent to opaque pink grossularite crystals in marble from Mexico

Grossular is a calcium-aluminium species of the garnet group of minerals. It has the chemical formula of Ca3Al2(SiO4)3 but the calcium may, in part, be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from the botanical name for the gooseberry, grossularia, in reference to the green garnet of this composition that is found in Siberia. Other shades include cinnamon brown (cinnamon stone variety), red, and yellow. Grossular is a gemstone.

Contents

In geological literature, grossular has often been called grossularite. Since 1971, however, use of the term grossularite for the mineral has been discouraged by the International Mineralogical Association. [4]

Hessonite

Striated crystals of hessonite, a variety of the grossular species Hessonite striated crytals.jpg
Striated crystals of hessonite, a variety of the grossular species

Hessonite or "cinnamon stone" is a common variety of grossular with the general formula: Ca3Al2Si3O12. The name comes from the Ancient Greek : ἣσσων (hēssōn), meaning inferior; [5] an allusion to its lower hardness and lower density than most other garnet species varieties. [2]

It has a characteristic red color, inclining to orange or yellow, much like that of zircon. It was shown many years ago, by Sir Arthur Herbert Church, that many gemstones, especially engraved gems (commonly regarded as zircon), were actually hessonite. The difference is readily detected by the specific gravity, that of hessonite being 3.64 to 3.69, while that of zircon is about 4.6. Hessonite has a similar hardness to that of quartz (being about 7 on the mohs scale), while the hardness of most garnet species is nearer 7.5. [5]

Hessonite comes chiefly from Sri Lanka and India, where it is found generally in placer deposits, though its occurrence in its native matrix is not unknown. [5] It is also found in Brazil and California.

Deposits

Grossular is found in contact metamorphosed limestones with vesuvianite, diopside, wollastonite and wernerite.

A highly sought after variety of gem garnet is the fine green Grossular garnet from Kenya and Tanzania called tsavorite. This garnet was discovered in the 1960s in the Tsavo area of Kenya, from which the gem takes its name.

Viluite is a variety name of grossular; that is not a recognized mineral species. [6] It is usually olive green though sometimes brownish or reddish, brought about by impurities in the crystal. Viluite is found associated with and is similar in appearance to vesuvianite, and there is confusion in terminology as viluite has long been used as a synonym for wiluite, a sorosilicate of the vesuvianite group. This confusion in nomenclature dates back to James Dwight Dana. [7] It comes from the Vilyuy river area in Siberia. A similar green grossular garnet can be found in the Wah Wah mountain range in Utah. [8]

Grossular is known by many other names, and also some misnomers; [9] colophonite – coarse granules of garnet, [10] ernite, gooseberry-garnet – light green colored and translucent, [11] olyntholite/olytholite, romanzovite, and tellemarkite. Misnomers include [3] South African jade, garnet jade, Transvaal jade, and African jade.

Cultural significance

In 1991, Vermont named grossular garnet its state gemstone. [12]

See also

Related Research Articles

<span class="mw-page-title-main">Spinel</span> Mineral or gemstone

Spinel is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl
2O
4 in the cubic crystal system. Its name comes from the Latin word spinella, a diminutive form of spine, in reference to its pointed crystals.

<span class="mw-page-title-main">Garnet</span> Mineral, semi-precious stone

Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.

<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">Cuprite</span>

Cuprite is an oxide mineral composed of copper(I) oxide Cu2O, and is a minor ore of copper.

<span class="mw-page-title-main">Uvarovite</span> Chromium-bearing garnet group

Uvarovite is a chromium-bearing garnet group species with the formula: Ca3Cr2(SiO4)3. It was discovered in 1832 by Germain Henri Hess who named it after Count Sergei Semenovitch Uvarov (1765–1855), a Russian statesman and amateur mineral collector. It is classified in the ugrandite group alongside the other calcium-bearing garnets andradite and grossular.

<span class="mw-page-title-main">Jadeite</span> Pyroxene mineral

Jadeite is a pyroxene mineral with composition NaAlSi2O6. It is hard (Mohs hardness of about 6.5 to 7.0), very tough, and dense, with a specific gravity of about 3.4. It is found in a wide range of colors, but is most often found in shades of green or white. Jadeite is formed only in the subduction zones of continental margins, where rock undergoes metamorphism at high pressure but relatively low temperature.

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

Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in dolomite and quartz. Tremolite forms a series with actinolite and ferro-actinolite. Pure magnesium tremolite is creamy white, but the color grades to dark green with increasing iron content. It has a hardness on Mohs scale of 5 to 6. Nephrite, one of the two minerals known as the gemstone jade, is a green variety of tremolite.

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

Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe)2Al3(Si5AlO18) to (Fe,Mg)2Al3(Si5AlO18). A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings.

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

Clintonite is a calcium magnesium aluminium phyllosilicate mineral. It is a member of the margarite group of micas and the subgroup often referred to as the "brittle" micas. Clintonite has the chemical formula Ca(Mg,Al)
3(Al
3Si)O
10(OH)
2. Like other micas and chlorites, clintonite is monoclinic in crystal form and has a perfect basal cleavage parallel to the flat surface of the plates or scales. The Mohs hardness of clintonite is 6.5, and the specific gravity is 3.0 to 3.1. It occurs as variably colored, colorless, green, yellow, red, to reddish-brown masses and radial clusters.

<span class="mw-page-title-main">Tsavorite</span> Variety of grossular

Tsavorite or tsavolite is a variety of the garnet group species grossular, a calcium-aluminium garnet with the formula Ca3Al2Si3O12. Trace amounts of vanadium or chromium provide the green color.

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

Vesuvianite, also known as idocrase, is a green, brown, yellow, or blue silicate mineral. Vesuvianite occurs as tetragonal crystals in skarn deposits and limestones that have been subjected to contact metamorphism. It was first discovered within included blocks or adjacent to lavas on Mount Vesuvius, hence its name. Attractive-looking crystals are sometimes cut as gemstones. Localities which have yielded fine crystallized specimens include Mount Vesuvius and the Ala Valley near Turin, Piedmont.

<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">Andradite</span> Nesosilicate mineral species of garnet

Andradite is a mineral species of the garnet group. It is a nesosilicate, with formula Ca3Fe2Si3O12.

<span class="mw-page-title-main">Aegirine</span> Member of the clinopyroxene group of inosilicate mineral

Aegirine is a member of the clinopyroxene group of inosilicate minerals. It is the sodium endmember of the aegirine–augite series. It has the chemical formula NaFeSi2O6, in which the iron is present as the ion Fe3+. In the aegirine–augite series, the sodium is variably replaced by calcium with iron(II) and magnesium replacing the iron(III) to balance the charge. Aluminum also substitutes for the iron(III). Acmite is a fibrous green-colored variety.

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

Wiluite is a dark green, brownish, or black blocky silicate mineral with the chemical formula Ca19(Al,Mg,Fe,Ti)13(B,Al,[ ])5Si18O68(O,OH)10. It has a Mohs hardness of 6 and a specific gravity of 3.36. It has a vitreous lustre, poor cleavage and an irregular brittle fracture. It crystallizes in the tetragonal system and occurs as well-formed crystals with good external form. It is isostructural with the vesuvianite group and is associated with wollastonite and olive-green grossulars (viluites) in a serpentinized skarn.

<span class="mw-page-title-main">Rhodolite</span> Rose-colored gemstone of the garnet group

Rhodolite is a varietal name for rose-pink to red mineral pyrope, a species in the garnet group. It was first described from Cowee Valley, Macon County, North Carolina. The name is derived from the Greek "rhodon" for "rose-like", in common with other pink mineral types. This coloration, and the commonly inclusion-free nature of garnet from this locality, has led to rhodolite being used as a gemstone. Rhodolite like other varietal names is not officially recognized as a mineralogical term, but rather used as an accepted trade name.

<span class="mw-page-title-main">Hydrogrossular</span> Calcium aluminium garnet

Hydrogrossular is a calcium aluminium garnet series (formula: Ca3Al2(SiO4)3−x(OH)4x, with hydroxide (OH) partially replacing silica (SiO4)). The endmembers of the hydrogarnet family (grossular, hibschite, and katoite) depend on the degree of substitution (x):

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

Howlite, a calcium borosilicate hydroxide (Ca2B5SiO9(OH)5), is a borate mineral found in evaporite deposits.

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 7 8 9 10 GIA Gem Reference Guide; Gemological Institute of America; 1995; ISBN   0-87311-019-6
  3. 1 2 Grossular The Mineral and Gemstone Kingdom, accessed online January 25, 2007
  4. ↑ International Mineralogical Association (1971). "International Mineralogical Association: Commission on new minerals and mineral names" (PDF). Mineralogical Magazine. 38 (293): 102–105. Bibcode:1971MinM...38..102.. doi:10.1180/minmag.1971.038.293.14.
  5. 1 2 3 Wikisource-logo.svg One or more of the preceding sentences incorporates text from a publication now in the public domain :  Chisholm, Hugh, ed. (1911). "Cinnamon-stone". Encyclopædia Britannica . Vol. 6 (11th ed.). Cambridge University Press. p. 376.
  6. ↑ Viluite Mindat database
  7. ↑ The System of Mineralogy of James Dwight Dana. Descriptive Mineralogy By James Dwight Dana, Edward Salisbury Dana, 1892, p. 479-80
  8. ↑ Mindat database, accessed 15 October 2023
  9. ↑ Grossular Mindat mineral database, accessed January 25, 2007
  10. ↑ Colophonite The Free Dictionary, accessed online January 25, 2007
  11. ↑ Gooseberry Garnet WordWeb Online
  12. ↑ "Vermont Emblems". State of Vermont. Archived from the original on 2009-10-29. Retrieved 2009-11-12.
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