16.8.1: Almandine
- Page ID
- 4131
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)
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
Figure \(\PageIndex{1}\): Oval, faceted Almandine garnet
Color
Brownish red, red to violet/purple
Spectroscope
Almandine has a typical iron spectrum.
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