Brianite

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Brianite
General and classification
other names

IMA 1966-030

chemical formula Na 2 CaMg [PO 4 ] 2
Mineral class
(and possibly department) 		Phosphates, arsenates, vanadates
System no. to Strunz
and to Dana 		8.AC.30 ( 8th edition : VII / A.05)
01/38/07/01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic 2 / m
Space group P 2 1 / a
Lattice parameters a  = 13.36  Å ; b  = 5.23 Å; c  = 9.13 Å
β  = 91.2 °
Formula units Z  = 4
Twinning polysynthetic twins according to {100}
Physical Properties
Mohs hardness 4 to 5
Density (g / cm 3 ) 3.0 to 3.3
Cleavage Please complete!
colour colorless
Line color White
transparency transparent
shine Please complete!
Crystal optics
Refractive indices n α  = 1.598
n β  = 1.605
n γ  = 1.608
Birefringence δ = 0.010
Optical character biaxial negative
Axis angle 2V = 63 to 65 °

Brianite is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the monoclinic crystal system with the chemical composition Na 2 CaMg [PO 4 ] 2 and has so far only been found in the form of 0.2 mm large crystals of negative V-shape or polysynthetic crystal twins with a lamellar structure according to {100}.


Etymology and history

Brianite was first found in 1967 in the Dayton meteorite near Dayton (Ohio) in the USA and described by LH Fuchs, E. Olsen and EP Henderson, who named the mineral in honor of Dr. Brian Harold Mason , a New Zealand-American geochemist, mineralogist and meteorite scientist, named after him.

classification

In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) , brianite belongs to the division of "anhydrous phosphates without foreign anions ". Since the new Strunz'schen mineral systematics, this department is more precisely divided according to the size of the cations . The mineral can now be found in the sub-section “anhydrous phosphates without foreign anions with medium-sized and large cations”, where it is the only member of the unnamed group “8.AC.30”.

The systematics of minerals according to Dana also assigns brianite to the class of phosphates, but there in the department of "anhydrous phosphates etc. with the general formula A + B 2+ XO 4 ", where it is also the only member of the unnamed group 38.01 .07 forms.

Education and Locations

Brianite forms as a rare component of phosphate needles in iron meteorites , often in paragenesis with panethite , for which the Dayton meteorite is also the type locality , but also with albite , enstatite , graphite , kamacite , writerite , sphalerite , taenite , troilite and whitlockite .

So far, brianite could only be detected in its type locality , the Dayton meteorite.

Crystal structure

Brianite crystallizes monoclinically in the space group P 2 1 / a with the lattice parameters a  = 13.36  Å ; b  = 5.23 Å; c  = 9.13 Å and β = 91.2 ° as well as four formula units per unit cell .

See also

Individual evidence

  1. ↑ a b c d e Handbook of Mineralogy - Brianite (English, PDF 64.2 kB)
  2. ↑ a b c d e Brianite at mindat.org (engl.)

literature

Web links