Crandallite

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Crandallite
Crandallite-162072.jpg
Tufts of needle-like crandallite from the Moculta phosphate quarry, Angaston , South Australia (size: 3.2 × 2.4 cm)
General and classification
chemical formula CaAl 3 [(OH) 6 | PO 3 (OH) | PO 4 ]
Mineral class
(and possibly department) 		Phosphates, Arsenates and Vanadates - Anhydrous phosphates with foreign anions
System no. to Strunz
and to Dana 		8.BL.10 ( 8th edition : VII / B.36)
07/22/03/01
Crystallographic Data
Crystal system trigonal (pseudocubic)
Crystal class ; symbol ditrigonal-scalenohedral; 3 2 / m
Room group (no.) R 3 m (No. 166)
Lattice parameters a  = 7.01  Å ; c  = 16.19 Å
Formula units Z  = 3
Physical Properties
Mohs hardness 5
Density (g / cm 3 ) 2.78 to 2.92
Cleavage is missing
Break ; Tenacity perfectly
colour white, gray, pale red, yellow
Line color White
transparency transparent to translucent
shine Glass gloss to matt
Crystal optics
Refractive indices n ω  = 1.618
n ε  = 1.623
Birefringence δ = 0.005
Optical character uniaxial positive

Crandallite is a relatively common mineral from the mineral class of anhydrous phosphates with foreign anions . It crystallizes in the trigonal crystal system with the chemical composition CaAl 3 [(OH) 6 | PO 3 (OH) | PO 4 ] and develops mostly granular to massive aggregates , but rarely also thin, fibrous crystals, often more than three millimeters in size, in white , gray, pale red, or yellow in color.

Etymology and history

Crandallit was named after the American engineer Milan L. Crandall Jr.

Crandallite was already described by B. Kosmann in the journal of the German Geological Society (Berlin: 21: 799) in 1869, but under the name "Kalkwavellit" in the chapter "The apatite from Offheim and the Kalkwavellit von Ahlbach and Dehrn". The mineral was not scientifically described under its recognized name until 1917 by GF Loughlin and Waldemar Theodore Schaller .

classification

In the now outdated 8th edition of the mineral classification according to Strunz , the crandallite belongs to the general division of "anhydrous phosphates with foreign anions ".

Since the revision of this system in the 9th edition , this section has been subdivided more precisely according to the size of the cations involved in the compound and their relationship to the anion complex (RO 4 ). Crandallite is found accordingly under the compounds “With medium-sized and large cations; (OH etc.): RO 4  = 3: 1 “.

The systematics of minerals according to Dana , which is common in English-speaking countries, also assigns the crandallite to the class of phosphates, but there in the division of " water-containing phosphates etc., with hydroxyl or halogen and the general composition (AB) 5 (XO 4 ) 3 Z q  • x (H 2 O) ", where he together with Gorceixit , Goyazit , Lusungit , Plumbogummit , Kintoreit , Benauit and Springcreekit the unnamed group 42.7.3 forms.

Varieties and modifications

The only known variety is the Eylettersite , which contains admixtures of thorium and fluoresces under UV light .

Education and Locations

Variscite (green) enclosed by crandallite (yellow), from the "Little Green Monster Variscite Mine", Clay Canyon, Fairfield , Oquirrh Mountains , Utah, USA (size: 7.8 × 7.3 × 0.4 cm)

Crandallite forms in weathered phosphate and aluminum-containing sediments and sedimentary rocks as well as in carbonatites . Accompanying minerals include fluoroapatite , hydroxyl herderite and quartz .

So far (as of 2010) the mineral has been found at around 220 sites around the world, including Angola ; New South Wales , South Australia and Tasmania in Australia; Belgium , Bolivia , Brazil , Burundi , Chile , China , Germany , Finland , France , Gabon , Guatemala , Ireland , Italy , Japan , Canada , Kazakhstan , Kyrgyzstan , Democratic Republic of the Congo , Kosovo , Mexico , Nigeria , Austria , Puerto Rico , Rwanda , Romania , Russia , Sweden , Senegal , Slovakia , Spain , Sri Lanka , Sudan South Africa , Togo , Czech Republic , Uganda , Hungary , Uzbekistan , the United Kingdom (Great Britain) and the United States (USA).

Crystal structure

Crandallite crystallizes trigonal in the space group R 3 m (space group no. 166) with the lattice parameters a  = 7.01  Å and c  = 16.19 Å as well as three formula units per unit cell .

See also

Individual evidence

  1. ↑ a b Webmineral - Crandallite (English)
  2. ↑ a b c d Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 462 .
  3. ↑ a b c d e Stefan Weiss: The great Lapis mineral directory . 4th edition. Christian Weise Verlag, Munich 2002, ISBN 3-921656-17-6 .
  4. ↑ a b c d e f Crandallite at mindat.org (engl.)
  5. ↑ Web archive: Full text of "Yearbooks of the Nassau Association for Natural History" - B. Kosmann. The apatite from Offheim and the lime wavellite from Ahlbach and Dehrn
  6. ^ Paul Ramdohr , Hugo Strunz : Klockmanns textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 634 .

Web links

Commons : Crandallit  - collection of images, videos and audio files