16.8.1: Almandina
- Page ID
- 90359
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|---|---|
| Composición química | Fe 3 Al 2 (SiO 4) 3 ron silicato de aluminio |
| Sistema de cristal | Cúbico |
| Hábito | Dodecaedros |
| Escote | Ninguno |
| Dureza | 7.5 |
| Naturaleza óptica | Isotrópico |
| Índice de refracción | 1.78-1.81 |
| Birrefringencia | Ninguno |
| Gravedad específica | 3.95 - 4.20 |
| Lustre | Vítreo |
Diagnósticos
Figura\(\PageIndex{1}\): Granate Almandino ovalado facetado
Color
Rojo parduzco, rojo a violeta/púrpura
Espectroscopio
La almandina tiene un espectro de hierro típico.
Figura\(\PageIndex{2}\): generalmente a 504, 520 y 573 nm, también puede tener líneas débiles a 423, 460, 610 y 680-690nm
Inclusiones
- Agujas cortas de rutilo en 3 direcciones
- Cristales rodeados de grietas por tensión
- Cristales irregulares y redondeados
Polariscopio
La almandina es isotrópica pero puede tener una DR pequeña.
Gravedad específica
La almandina se hunde en todos los líquidos pesados comunes.
Efectos ópticos
El almandina puede mostrar asterismo y chatoyancia.
Variedades
Rodolita
La rodolita es la variedad púrpura (rosa/violeta) de pirope-almandina.
Localidades
India, Estados Unidos, Brasil
Ocurrencia
Rocas metamórficas