Cafetite

Cafetite
Yellow cafetite crystals with green lizardite and calcite
General
Category oxide mineral
Formula
(repeating unit)		 (Ca,Mg)(Ti,Al)2O4(OH)2
Strunz classification 4.FL.75
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/n
Unit cell a = 4.944 Å,
b = 12.109 Å,
c = 15.911 Å;
β= 98.93°; Z = 8[1]
Identification
Color Pale yellow to colorless
Crystal habit Elongated columnar to acicular crystals, fibrous aggregates, pseudo-orthorhombic
Cleavage Prismatic
Tenacity Brittle
Mohs scale hardness 4-5
Luster Adamantine
Streak White
Diaphaneity Semitransparent
Specific gravity 3.28
Optical properties Biaxial (–), 2V=58°, Dispersion very strong, r > v
Refractive index nα = 1.95, nβ = 2.08, nγ = 2.11
Birefringence δ = 0.16
Pleochroism none
2V angle Measured: 38°
References [1][2][3][4]

Cafetite is a rare titanium oxide mineral with formula (Ca,Mg)(Fe,Al)2Ti4O12·4(H2O). It is named for its composition, Ca-Fe-Ti.[4]

It was first described in 1959 for an occurrence in the Afrikanda Massif, Afrikanda, Kola Peninsula, Murmanskaja Oblast', Northern Region, Russia.[3][2] It is also reported from the Khibiny and Kovdor massifs of the Kola Peninsula and from Meagher County, Montana, US.[3]

It occurs in pegmatites in a pyroxenite intrusion as crystals in miarolitic cavities. It occurs associated with ilmenite, titaniferous magnetite, titanite, anatase, perovskite, baddeleyite, phlogopite, clinochlore and kassite.[2]

References

  1. 1 2 Mineralienatlas
  2. 1 2 3 Handbook of Mineralogy
  3. 1 2 3 Mindat.org
  4. 1 2 Webmineral.com
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