Aenigmatite

Aenigmatite
General
Category	Silicate mineral
Chemical formula	Na2Fe2+5TiSi6O20
Strunz classification	9.DH.40
Crystal symmetry	Triclinic pinacoidal H-M symbol: 1 Space group: P1
Unit cell	a = 10.415(1) Å, b = 10.840(1) Å, c = 8.931(1) Å; α = 105.107(4)°, β = 96.610(5)°, γ = 125.398(4)°; Z = 2
Identification
Color	Velvet-black
Crystal habit	Poorly developed prismatic crystals, occurring as irregular clusters
Crystal system	Triclinic - pseudomonoclinic
Twinning	Complex by rotation perpendicular to (011) or about [010] of the pseudomonoclinic cell; polysynthetic
Cleavage	Good on {010} and {100}
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	5.5
Luster	Vitreous to greasy
Streak	Reddish brown
Diaphaneity	Translucent to opaque
Specific gravity	3.81
Optical properties	Biaxial (+)
Refractive index	nα = 1.780 - 1.800 nβ = 1.800 - 1.820 nγ = 1.870 - 1.900
Birefringence	δ = 0.090 - 0.100
Pleochroism	X = yellow brown; Y = red-brown; Z = dark brown to black
2V angle	Measured: 27° to 55°
Dispersion	r < v; very strong
References	[1][2][3]

Aenigmatite, also known as Cossyrite after Cossyra, the ancient name of Pantelleria, is a sodium, iron, titanium inosilicate mineral. The chemical formula is Na₂Fe²⁺₅TiSi₆O₂₀ and its structure consists of single tetrahedral chains with a repeat unit of four and complex side branches. It forms brown to black triclinic lamellar crystals. It has Mohs hardness of 5.5 to 6 and specific gravity of 3.74 to 3.85. Aenigmatite forms a solid-solution series with wilkinsonite, Na₂Fe²⁺₄Fe³⁺₂Si₆O₂₀.

Aenigmatite is primarily found in peralkaline volcanic rocks, pegmatites, and granites as well as silica-poor intrusive rocks. It was first described by August Breithaupt in 1865 for an occurrence in the Ilimaussaq intrusive complex of southwest Greenland. Its name comes from αίνιγμα, the Greek word for "riddle".

It was also reported from the Kaidun meteorite, possibly a Mars meteorite, which landed on March 1980 in South Yemen. Other notable studied occurrences include:

• Narsaarsuk and elsewhere in Greenland.
• The Khibiny and Lovozero alkaline massifs on Kola Peninsula, Russia.
• The volcanic island of Pantelleria, Italy.
• In the USA, from Granite Mountain, near Little Rock, Pulaski County, Arkansas, and Santa Rosa, Sonoma County, California.
• In Australia, from Warrumbungle volcano, Nandewar volcano, and the Mount Warning complex, New South Wales; and the Peak Range Province, Queensland.
• In Canada, from Mount Edziza, the Ilgachuz and Rainbow Range shield complexes.
• From Logan Point quarry, Dunedin volcano, New Zealand.

References

1. ^ Mindat with location data
2. ^ Webmineral data
3. ^ Handbook of Mineralogy

This article about a specific silicate mineral is a stub. You can help Wikipedia by expanding it.v · Categories: Sodium minerals Iron minerals Titanium minerals Inosilicates Triclinic minerals Silicate mineral stubs Wikimedia Foundation. 2010. Игры ⚽ Нужно решить контрольную? Radio Rennes Bretagne Papineauville, Quebec Look at other dictionaries: aenigmatite — noun An inosilicate mineral of sodium, iron, and titanium, forming brown to black triclinic lamellar crystals. Syn: cossyrite …   Wiktionary aenigmatite — variant of enigmatite …   Useful english dictionary Aenigmatit — Chemische Formel Na2(Fe2+4Ti)Fe2+[O2|Si6O18] [1] Mineralklasse Silikate und Germanate Ketten und Bandsilikate 9.DH.40 (8. Auflage: VIII/F.14 20) (nach Strunz) 69.02.01a.01 (nach Dana) Kristallsystem …   Deutsch Wikipedia List of minerals A-B (complete) — It is currently not possible to have a complete list of minerals . The International Mineralogical Association is the international group that recognises new minerals and new mineral names, however minerals discovered before 1959 did not go… …   Wikipedia Mount Edziza volcanic complex — Mount Edziza, one of the main volcanoes of the Mount Edziza volcanic complex Elevation …   Wikipedia Энигматит — Формула Na2Fe2+5Ti4+O2[Si6O18] Сингония триклинная Цвет темно коричневый до густо черного Цвет черты темно бурая с красноватым оттенком Блеск матовый Твёрдость 5,5 6 Излом неровный Плотность 3,73 3,85 г/см³ …   Википедия Mineral — For other uses, see Mineral (disambiguation). An assortment of minerals. A mineral is a naturally occurring …   Wikipedia Rutile — Wine red rutile crystals from Binn Valley, Switzerland (Size: 2.0 x 1.6 x 0.8 cm) General Category Oxide minerals …   Wikipedia Ilmenite — from Miask, Ilmen Mts, Chelyabinsk Oblast , Southern Urals, Urals Region, Russia. 4.5 x 4.3 x 1.5 cm General Category Oxide mineral …   Wikipedia List of minerals — This is a List of minerals for which there are Wikipedia articles. Mineral variety names and mineraloids are to be listed after the valid minerals for each letter.For a complete listing (about 4,000) of all mineral names: List of minerals… …   Wikipedia 18+ © Academic, 2000-2024 Contact us: Technical Support, Advertising Dictionaries export, created on PHP, Joomla, Drupal, WordPress, MODx. Mark and share Search through all dictionaries Translate… Search Internet Share the article and excerpts Direct link … Do a right-click on the link above and select “Copy Link”