Montebrasite | Gemopedia

Montebrasite is a light green to yellow or colorless gemstone that belongs to the amblygonite group. Similar to amblygonite in chemical composition, it has less fluorine content and twinned crystals are common. Montebrasite was named for its discovery in Montebras, France.
Colors
Colorless, Yellow-Green, Light Green, Light Blue, Pink, Pale Brown, Grayish White

Montebrasite Classification

Common Name

Montebrasite

Species

Montebrasite

Variety

Colors

Colorless, Yellow-Green, Light Green, Light Blue, Pink, Pale Brown, Grayish White

Alternate Names

Gemstone Groups

Amblygonite

Key Separations

RI, the lowest RI value of montebrasite 1.594 is lower than RI of 1.612 of amblygonite.

Comments

Often misidentified as amblygonite.

Montebrasite Optical Properties

Transparency

Transparent

Refractive Index

1.594-1.633

Birefringence

0.02-0.022

Optic Character

Biaxial

Optic Sign

Positive

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert
LWUV: Inert to weak green

CCF Reaction

Pleochroism

Unobservable

Dispersion

Comments

Montebrasite Chemistry & Crystallography

Chemical Name

lithium sodium aluminum phosphate

Chemical Formula

LiAl(PO4)(OH,F)

Synthesis

Crystal System

Trigonal

Classification

Phosphate

Nature

Natural

Crystallinity

Crystalline

Comments

Montebrasite Characteristic Physical Properties

Hardness

5.5-6

Streak

White

Specific Gravity

2.98-3.11

Toughness

Poor

Inclusions

Luster

Vitreous

Stability

Fracture

Uneven, Subconchoidal

Cleavage

Perfect, in one direction, Good, in two directions

Comments

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