Andalusite natural mine rough crystal Brazil color shift 125 carats Rare mineral

Description

125 carat ,,,25 gram...,,lots of  crystal all natural  mine rough andalusite from Brazil and generally sized from 3 to 12 MM in length/width and 2 to 5 MM in depth and grade mixed from cab to facet most included partially with some pieces having areas of nice clean facet material.M
ine rough andalusite crystal,sometimes called "poor mans alexandrite" due to the yellow/green/red color shifts,with a 7 1/2 mohs hardness
.
Faceted andalusite stones give a play of red, green, and yellow colors that resembles a muted form of
iridescence
, although the colors are actually the result of unusually strong
pleochroism
.
Each lot will be scooped from material as pictured and the pictures were taken without flash and dry.
Shipping in the US mainland will be FREE by USPS first class.
Category
Nesosilicates
Formula
(repeating unit)
Al
2
SiO
5
Strunz classification
09.AF.10
Crystal symmetry
2/m 2/m 2/m - Dipyramidal
Unit cell
a = 7.7980
Å
b = 7.9031 Å c = 5.5566 Å; Z = 4
Color
Pink, violet, yellow, green, white, gray; in thin section, colorless to pink or green
Crystal habit
As euhedral crystals or columnar aggregates having nearly square cross sections; fibrous compact to massive
Crystal system
orthorhombic
Mohs scale
hardness
6.5 - 7.5
Luster
Vitreous
Streak
White
Diaphaneity
Transparent to nearly opaque with inclusions
Specific gravity
3.17 (+/- .04)
Optical properties
double refractive, biaxial negative;
chiastolite
has anomalous aggregate reaction.
[1]
Refractive index
n
α
= 1.629 - 1.640 n
β
= 1.633 - 1.644 n
γ
= 1.638 - 1.650
Birefringence
δ = 0.009 - 0.010
Pleochroism
strongly trichroic
2V angle
71 - 86°
Dispersion
r < v strong
Ultraviolet
fluorescence
non-fluorescent
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