Mineral - Barroisite
Barroisite
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
[Na,Ca][(Mg,Fe²⁺)₃Al₂](Si₇Al)O₂₂(OH)₂
Unit Cell
a=9.76 b=17.92 c=5.29 β=105° Z=2
Physical Properties
Hardness
5 - 6
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {110}, intersecting at 54.5° and 125.5°
Fracture
Tenacity
Brittle
Optical Properties
Color
blackbrowngreengreen black
Birefringence
Luster
Vitreous
Transparency
opaque
Pleochroism
Geomineralogical Properties
Crystal System
monoclinic
Point Group
monoclinic-prismatic - 2/m
Space Group
C2/m (12)
Habit
coarse, massive, acicular, prismatic, tabular
Formation
Through blueschist-facial metamorphism
Paragenesis
Twinning
Rarity
Very rare
Synonyms
Barroisite
Composition
Elements
Mass
SiO₂
53.26
TiO₂
0.24
Al₂O₃
7.90
Cr₂O₃
0.04
FeO
5.80
MnO
0.03
NiO
0.11
MgO
17.84
CaO
7.41
Na₂O
3.84
K₂O
0.39
F
0.04
Cl
0.03
Norway (Murgoci 1922)
Groups and Members
Amphibole-Supergroup
Na-Ca-Amphibole-Group
Barroisite (Bar) Amphibole-Subgroup
Name and first discovery: Named after the French geologist Charles Eugene Barrois (1851-1939). First described in 1922.
Chemism:
Synonyms:
Varieties:
Abbreviation: Brs
As with other amphiboles, information on this mineral should be treated with caution. Samples that have not been analysed are often other end members, such as oxo-magnesio-hastingsite.
Literature
Murgoci, G. (1922) Sur les propriétés des amphiboles bleues. Compt. Rendus Acad. Sci. Paris, 175, 373.