16.8.1: Almandine

Gemology · LibreTexts

0%

Contents

    Text

    Size
    100%
    Theme
    Typeface
    Line length
    Spacing

    From LibreTexts, under CC BY-NC-SA 2.5, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.

    Almandine Garnet
    Chemical composition Fe3Al2(SiO4)3ron aluminum silicate
    Crystal system Cubic
    Habit Dodecahedra
    Cleavage None
    Hardness 7.5
    Optic nature Isotropic
    Refractive index 1.78-1.81
    Birefringence None
    Specific gravity 3.95 - 4.20
    Lustre Vitreous

    Diagnostics

    File:Almandine.jpg

    Figure \(\PageIndex{1}\): Oval, faceted Almandine garnet

    Color

    Brownish red, red to violet/purple

    Spectroscope

    Almandine has a typical iron spectrum.

    File:Almandine spectrum.jpg

    Figure \(\PageIndex{2}\): usually at 504, 520, and 573nm, may also have faint lines at 423, 460, 610 and 680-690nm

    Inclusions

    • Short rutile needles in 3 directions
    • Crystals surrounded by stress cracks
    • Irregular and rounded crystals

    Polariscope

    Almandine is isotropic but may have a small DR.

    Specific gravity

    Almandine sinks in all common heavy liquids.

    Optical effects

    Almandine may show asterism and chatoyancy.

    Varieties

    Rhodolite

    Rhodolite is the purple (pinkish/violet) variety of pyrope-almandine.

    Localities

    India, USA, Brazil

    Occurrence

    Metamorphic rocks

    This page titled 16.8.1: Almandine was last modified on Fri, 06 May 2022 23:29:24 GMT and is shared under a CC BY-NC-SA 2.5 license and was authored, remixed, and/or curated by gemology via source content that was edited to the style and standards of the LibreTexts platform.