Cyclosilicates

thumb|upright=1.3|Main tourmaline producing countries

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: to . A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the rings. Cordierite is also synthesized and used in high temperature applications such as catalytic converters and pizza stones.

Dioptase is an intense emerald-green to bluish-green mineral that is cyclosilicate of copper. It is transparent to translucent. Its luster is vitreous to sub-adamantine. Its formula is , also reported as . It has a Mohs hardness of 5, the same as tooth enamel. Its specific gravity is 3.28–3.35, and it has two perfect and one very good cleavage directions. Additionally, dioptase is very fragile, and specimens must be handled with great care. It is a trigonal mineral, forming six-sided crystals that are terminated by rhombohedra.

Benitoite () is a rare, blue, barium titanium cyclosilicate mineral, found in hydrothermally altered serpentinite. It forms in low-temperature, high-pressure environments typical of subduction zones at convergent plate boundaries. Benitoite fluoresces under short-wave ultraviolet light, appearing bright blue to bluish white in color. The more rarely seen clear to white benitoite crystals fluoresce red under long-wave UV light.

thumb|Pink eudialyte in syenite ([[lujavrite) from Poços de Caldas, Brazil. The white mineral is alkali feldspar, the black is aegirine, and the little brown bits are biotite.]]

Elbaite, a sodium, lithium, aluminium boro-silicate, with the chemical composition Na(Li1.5Al1.5)Al6Si6O18(BO3)3(OH)4, is a mineral species belonging to the six-member ring cyclosilicate tourmaline group.

Sugilite ( ) is a relatively rare pink to purple cyclosilicate mineral with the complex chemical formula KNa2(Fe, Mn, Al)2Li3Si12O30. Sugilite crystallizes in the hexagonal system with prismatic crystals. The crystals are rarely found and the form is usually massive. It has a Mohs hardness of 5.5–6.5 and a specific gravity of 2.75–2.80. It is mostly translucent. Sugilite was first described in 1944 by the Japanese petrologist Ken-ichi Sugi (1901–1948) for an occurrence on Iwagi Islet, Japan, where it is found in an aegirine syenite intrusive stock. It is found in a similar environment at

Bazzite is a beryllium scandium cyclosilicate mineral with chemical formula ( or ). It crystallizes in the hexagonal crystal system typically as small blue hexagonal crystals up to 2 cm length. It has a Mohs hardness of 6.5–7 and a specific gravity of 2.77 to 2.85.

Pezzottaite, marketed under the name raspberyl or raspberry beryl, is a mineral species first recognized by the International Mineralogical Association in September 2003. Pezzottaite is a caesium analogue of beryl, a silicate of caesium, beryllium, lithium and aluminium, with the chemical formula Cs(Be2Li)Al2Si6O18. Named after Italian geologist and mineralogist Federico Pezzotta, pezzottaite was first thought to be either red beryl or a new variety of beryl ("caesium beryl"); unlike actual beryl, however, pezzottaite contains lithium and crystallizes in the trigonal crystal system rather than

Osumilite is a very rare potassium-sodium-iron-magnesium-aluminium silicate mineral. Osumilite is part of the milarite group (also known as the milarite-osumilite group) of cyclosilicates.

Papagoite is a rare cyclosilicate mineral. Chemically, it is a calcium copper aluminium silicate hydroxide, found as a secondary mineral on slip surfaces and in altered granodiorite veins, either in massive form or as microscopic crystals that may form spherical aggregates. Its chemical formula is Ca Cu Al Si2O6(O H)3.

Fluor-uvite is a tourmaline mineral with the chemical formula CaMg3(Al5Mg)(Si6O18)(BO3)3(OH)3F. It is a rare mineral that is found in calcium rich contact metamorphic rocks with increased amounts of boron. Uvite is trigonal hexagonal, which means that it has three equal length axes at 120 degrees, all perpendicular to its fourth axis which has a different length. Uvite is part of the space group 3m. Uvite's hardness has been measured to be 7.5 on the Mohs hardness scale. The color of uvite widely varies, depending on the sample, but is mostly deep green or brown. In regard to uvite's optical p

Fluor-buergerite, originally named buergerite, is a mineral species belonging to the tourmaline group. It was first described for an occurrence in rhyolitic cavities near Mexquitic, San Luis Potosi, Mexico. It was approved as a mineral in 1966 by the IMA and named in honor of Martin J. Buerger (1903–1986), professor of mineralogy at the Massachusetts Institute of Technology. It has also been reported from Minas Gerais, Brazil, and the Central Bohemia Region of the Czech Republic.

Poudretteite is an extremely rare mineral and gemstone that was first discovered as minute crystals in Mont St. Hilaire, Quebec, Canada, during the 1960s. The mineral was named for the Poudrette family because they operated a quarry in the Mont St. Hilaire area where poudretteite was originally found, and the quarry is currently owned by the United Kingdom based Salmon Mining Industries Inc. Poudretteite has a barely detectable radioactivity.

Baotite is a rare mineral with the chemical formula Ba4Ti4(Ti, Nb, Fe)4(Si4O12)O16Cl, recognized as having a unique four-fold silicate ring. Crystals are tetragonal, though commonly deformed to the extent of appearing monoclinic. Named for the locality of first discovery, Baotou, China, baotite has been found in hydrothermal veins and alkalic rocks in various locations around the world.

Nenadkevichite is a rare silicate mineral containing niobium with the chemical formula . It forms brown to yellow to rose colored orthorhombic dipyramidal crystals with a dull to earthy luster. It has a Mohs hardness of 5 and a specific gravity of 2.86.

Povondraite is a rare silicate mineral from the tourmaline group with formula: NaFe3+3(Fe3+4,Mg2)(BO3)3Si6O18(OH)3O. It is a dark brown to black nearly opaque mineral with a resinous to splendent luster. It crystallizes in the trigonal crystal system as equant, distorted prisms with trigonal pyramid terminations.

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

Almarudite (IMA symbol: Alr) is an extremely rare alkaline manganese beryllium silicate mineral of the cyclosilicates (ring silicates) class, with the chemical formula , from the volcanic environment of the Eifel Mountains in Germany.

Steacyite is a complex silicate mineral containing thorium and uranium; formula . It forms small brown or yellow green crystals, often cruciform twinned crystals. It is radioactive. It was discovered at Mont-Saint-Hilaire, Quebec in 1982 and is named after Harold Robert Steacy (1923–2012), mineralogist.

Kainosite is a silicate mineral that has the formula of Ca2(Y,Ce) SiO4O12(CO3)•(H2O). Kainosite was first discovered in Norway on the island of Hitterø and was named by Adolf Erik Nordenskiöld (1832–1901) in allusion to the Greek word for "unusual" for its rarity and exotic composition.

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 Fluor-liddicoatite Ca(Li2Al)Al6(BO3)3Si6O18(OH)3F Elbaite Na(Al1.5Li1.5)A

Raslakite is a rare mineral of the eudialyte group with the chemical formula . This formula is based on the original one, and is extended to show the presence of cyclic silicate groups. The additional silicon and oxygen shown in separation from the cyclic groups (in parentheses) are in fact connected with two 9-fold rings. The mineral has lowered symmetry (space group R3, instead of more specific for the group R3m one), similarly to some other eudialyte-group members: aqualite, labyrinthite, oneillite and voronkovite. The specific feature of raslakite is, among others, the presence of sodium a

Aqualite is a very rare mineral of the eudialyte group, with formula (H3O)8(Na,K,Sr)5Ca6Zr3SiSi(Si24O66)(OH)9Cl. The formula given does not show the presence of cyclic silicate groups. The original formula was extended to show the presence of silicon at both M3 and M4 sites, according to the nomenclature of the eudialyte group. Aqualite is unique among the eudialyte group in being hydronium-rich (the only other eudialyte-group species with essential hydronium, is the recently discovered ilyukhinite). Among the other representatives of the group it also distinguish in splitting of the M1 site i

Ikranite is a member of the eudialyte group, named after the Shubinov Institute of Crystallography of the Russian Academy of Sciences. It is a cyclosilicate mineral that shows trigonal symmetry with the space group R3m, and is often seen with a pseudo-hexagonal habit. Ikranite appears as translucent and ranges in color from yellow to a brownish yellow. This mineral ranks a 5 on Mohs scale of mineral hardness, though it is considered brittle, exhibiting conchoidal fracture when broken.

Combeite is a rare silicate mineral with the formula Na2Ca2Si3O9. It has a trigonal crystal system.

Khomyakovite is an exceedingly rare mineral of the eudialyte group, with formula . The original formula was extended to show the presence of both the cyclic silicate groups and M4-site silicon, according to the nomenclature of the eudialyte group. Some niobium substitutes for tungsten in khomyakovite. Khomyakovite is an iron-analogue of manganokhomyakovite, the second mineral being a bit more common. The two minerals are the only group representatives, beside taseqite, with species-defining strontium, although many other members display strontium diadochy. Khomyakovite is the third eudialyte-g

Baratovite is a very rare cyclosilicate mineral named after Rauf Baratovich Baratov from Tajikistan. It was discovered in 1974 at Dara-Pioz glacier, Tajikistan, and was approved by the International Mineralogical Association only a year later in 1975. The glacier gives home to 133 valid species, and is the type locality of 33 minerals, one of which is baratovite.

Lucchesiite is a new member of tourmaline-group of minerals. Lucchesiite has the formula CaFe3Al6(Si6O18)(BO3)3(OH)3O. It is the calcium and oxygen-analogue of schorl. It has two co-type localizations, one in Czech Republic and the other in Sri Lanka. As the other members of the tourmaline group, it is trigonal.

Yagiite is a cyclosilicate mineral belonging to the osumilite group. It was discovered in 1968 in the iron meteorite that fell in Colomera in the province of Granada (Spain). Named after the Japanese mineralogist Kenzo Yagi, its CAS Registry Number is IMA1968-020.

Katayamalite is a cyclosilicate mineral that was named in honor of mineralogist and professor Nobuo Katayama. It was approved in 1982 by the International Mineralogical Association, and was first published a year later.

Tienshanite, named for the Tian Shan Range in Mongolia, is a rare borosilicate mineral, though rock-forming in some parts of its original locality at the Dara-i-Pioz Glacier in Tajikistan. Its formula is extremely complex: .

Zirsilite-(Ce) is a very rare mineral of the eudialyte group, with formula . The original formula was extended to show the presence of cyclic silicate groups and the presence of silicon at the M4 site, according to the nomenclature of the eudialyte group. Zirsilite-(Ce) differs from carbokentbrooksite in cerium-dominance over sodium only. Both minerals are intimately associated. The only other currently known representative of the eudialyte group having rare earth elements (in particular cerium, as suggested by the "-Ce)" Levinson suffix in the name) in dominance is johnsenite-(Ce).

Alluaivite is a rare mineral of the eudialyte group, with complex formula written as . It is unique among the eudialyte group as the only titanosilicate (other representatives of the group are usually zirconosilicates). The two dual-nature minerals of the group, being both titano- and zirconosilicates, are labyrinthite and dualite. They both contain alluaivite module in their structures. Alluaivite is named after Mt. Alluaiv in Lovozero Tundry massif, Kola Peninsula, Russia, where it is found in ultra-agpaitic, hyperalkaline pegmatites.

Ashburtonite is a rare lead copper silicate-bicarbonate mineral with formula: HPb4Cu2+4Si4O12(HCO3)4(OH)4Cl.

Georgbarsanovite is a very rare mineral of the eudialyte group, formerly known under unaccepted name as barsanovite, with formula . The original formula was extended to show the presence of cyclic silicate groups and the domination of silicon at the M4 site. "REE", standing for rare earth elements, is dominated by cerium. Georgbarsanovite is characterized in dominance of manganese at the N4 site. It also differs from most other accepted group representatives in its colour. The mineral was found in nepheline pegmatite near Petrelius River, Khibiny massif, Kola Peninsula, Russia. It is named aft

Feklichevite is a rare mineral of the eudialyte group with the formula Na11Ca9(Fe3+,Fe2+)2Zr3NbSi(Si3O9)2(Si9O27)2. The original formula was extended to show the presence of cyclic silicate groups and presence of silicon at the M4 site, according to the nomenclature of eudialyte group. When compared to other minerals of the group, feklichevite characterizes in the presence of ferric iron (thus similar to ikranite, mogovidite and fengchengite) and dominance of calcium at the N4 site. Calcium is ordered in the structure and is also present at the M1 site. Other iron-bearing minerals of the group

Kentbrooksite is a moderately rare mineral of the eudialyte group, with chemical formula . This extended formula shows the presence of cyclic silicate groups and dominance of Si at the M4 site, according to the nomenclature of the eudialyte group. The characteristic features of kentbrooksite, that make it different from eudialyte are: (1) dominancy of fluorine (the only currently known example among the whole group), (2) dominancy of manganese, and (3) dominancy of niobium. Trace hafnium and magnesium are also reported. Kentbrooksite is relatively common when compared to most other species of

Fengchengite is a rare mineral of the eudialyte group with the formula . The formula is simplified as it does not show the presence of cyclic silicate groups. When compared to other minerals of the group, fengchengite characterizes in the presence of ferric iron (thus similar to ikranite, mogovidite and feklichevite) and essential, site-dominating vacancies. The mineral was discovered in the Saima complex near Fengcheng city in China – hence its name.

Andrianovite is a very rare mineral of the eudialyte group, with formula Na12(K,Sr,Ce)6Ca6(Mn,Fe)3Zr3NbSi(Si3O9)2(Si9O27)2O(O,H2O,OH)5. The original formula was extended to show the presence of cyclic silicate groups and silicon at the M4 site, according to the nomenclature of eudialyte group. Andrianovite is unique among the eudialyte group in being potassium-rich (other eudialyte-group species with essential K are davinciite and rastsvetaevite). It is regarded as potassium analogue of kentbrooksite, but it also differs from it in being oxygen-dominant rather than fluorine-dominant. Also, the

Pseudowollastonite is a high-temperature mineral phase of CaSiO3 and is polymorphous with wollastonite. Its formula can alternatively be written as Ca3Si3O9. Other names include ß-Wollastonite, and cyclowollastonite.

Pabstite is a barium tin titanium silicate mineral that is found in contact metamorphosed limestone. It belongs to the benitoite group of minerals. The chemical formula of pabstite is . It is found in Santa Cruz, California. The crystal system of the mineral is hexagonal.

Manganoeudialyte is an moderately rare mineral of the eudialyte group, with formula Na14Ca6Mn3Zr3Si2[Si24O72(OH)2]Cl2·4H2O. The formula given is one of the forms that can be given, based on the originally reported one, and shows dominance of silicon at both the M3 and M4 sites. As suggested by its name, it is the manganese-analogue of eudialyte.

Dualite is a very rare and complex mineral of the eudialyte group, its complexity being expressed in its formula . The formula is simplified as it does not show the presence of cyclic silicate groups. The name of the mineral comes from its dual nature: zircono- and titanosilicate at once. Dualite has two modules in its structure: alluaivite one and eudialyte one. After alluaivite and labyrinthite it stands for third representative of the eudialyte group with essential titanium.

Manganokhomyakovite is a very rare mineral of the eudialyte group, with the chemical formula . This formula is in extended form (based on the original one), to show the presence of cyclic silicate groups and domination of silicon at the M4 site, basing on the nomenclature of the eudialyte group. Some niobium substitutes for tungsten in khomyakovite. As suggested by its name, manganokhomyakovite is a manganese-analogue of khomyakovite, the latter being more rare. The two minerals are the only group representatives, beside taseqite, with species-defining strontium, although many other members di

Davinciite is a very rare mineral of the eudialyte group, with the simplified formula Na12K3Ca6Fe32+Zr3(Si26O73OH)Cl2. The formula given does not show the presence of cyclic silicate groups. The mineral was named after Leonardo da Vinci to refer to the atypical geometrical forms he tended to use, compared by the authors of the mineral description to the atypical (not ideally centrosymmetrical) geometry of the Davinciite structure. The other quite atypical feature of Davinciite is its lavender colour, while the typical eudialyte is rather pink or red.

Ferrokentbrooksite is a moderately rare mineral of the eudialyte group, with formula . The original formula was extended form to show the presence of cyclic silicate groups and presence of silicon at the M4 site, according to the nomenclature of eudialyte group. As suggested by its name, it is the (ferrous) iron analogue of kentbrooksite. When compared to the latter, it is also chlorine-dominant instead of being fluorine-dominant. The original (holotype) material is also relatively enriched in rare earth elements, including cerium and yttrium.

Alsakharovite-Zn (IMA symbol: Ask-Zn) is an extremely rare alkaline strontium zinc titanium silicate mineral from the cyclosilicates class, with the chemical formula , from alkaline pegmatites. It belongs to the labuntsovite group.

Klöchite is a cyclosilicate mineral of the Osumilite Group, found in a basalt quarry in Klöch, Austria. The basalt quarry it was found in is part of the Styrian Basin Volcanic Field in south-eastern Austria. Klöchite was found to be hosted in a xenolith primarily composed of quartz, sanidine, and diopside. Very few vesicles in the xenolith held Klöchite crystals, and only two samples were taken for study.

Rastsveatevite is a rare mineral of the eudialyte group with the chemical formula . Its structure is modular. It is only the third member of the group after andrianovite and davinciite with essential (site-dominating) potassium. Potassium and sodium enter both N4 and M2 sites. The mineral is named after Russian crystallographer Ramiza K. Rastsvetaeva.