16.8.4: Pyrope
- Page ID
- 4135
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|---|---|
| Chemical composition | Mg3Al2(SiO4)3agnesium aluminum silicate |
| Crystal system | Cubic |
| Habit | Dodecahedra |
| Cleavage | None |
| Hardness | 7.0-7.5 |
| Dispersion | Medium, 0.022 |
| Optic nature | Isotropic |
| Refractive index | 1.730-1.760 |
| Birefringence | None |
| Specific gravity | 3.65-3.80 |
| Lustre | Vitreous |
Pyrope is a red, orange-red, brownish-red to pink species of the garnet group which forms isomorphous series with almandine, spessartite and grossular. Pyrope, like all other species of the garnet group, is seldom seen having its ideal chemical makeup.
Diagnostics
Spectroscope
Pyrope has a chromium spectrum that can be combined with the typical spectrum of almandine.
Inclusions
- Rounded crystals of low relief
- Rutile needles
Polariscope
Pyrope (in all its isomorphous series) may show anomalous birefringence.
Refractometer
The refraction index of pyrope is 1.714 but, because it is never found pure, its index has a lower value of 1.730 and an upper value of 1.760.
Pyrope is singly refractive (isotropic).
Specific gravity
Pure pyrope has a specific gravity of 3.58. Due to isomorphous replacement, this value is never measured. Instead, its value ranges from 3.65 to 3.80.
Pyrope sinks in all common heavy liquids.
Varieties
Rhodolite
Rhodolite is the purple variety of pyrope-almandine. The name and color come from the flower of the rhodondendron.
The jewelry trade sometimes describes every purple garnet as a rhodolite but it should be reserved only for those having an intermediate chemical composition between pyrope and almandine.
Malaia
Malaia garnet (or malaya) is the red-orange variety of pyrope-spessartite discovered in the 1970's in Kenia as a by-product of rhodolite.
The name is derived from the Swahili word for prostitute (which freely translates to "outcast" or "out of the family") [see: Swahili - English Dictionary; Rouse, 1986].
Localities
- South-Africa
- USA
- Russia
References
- Swahili - English Dictionary
- Garnet (1986) - John D. Rouse ISBN 0408015349