| General Formula: X3Y2(SiO4)3 where
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Sample: PT-104 | System: Isometric |
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| Garnet Porphyroblasts Three anhedral garnet porphyroblasts associated with biotite, staurolite, and muscovite from a Meguma Group pelite. Field of view = 2.7 mm, plane light |
Garnet Porphyroblasts The isotropic nature of the garnet is obvious as are the inclusions of quartz, the trails of which are approximately parallel to the fabric (running from top right to lower left). Field of view = 2.7 mm, crossed polars |
Block diagram showing the relationship between the crystallographic axes and the indicatrix axes. |
Optical Properties
| Colour Pleochroism |
commonly colourless or a pale version of the hand sample non pleochroic |
Form | euhedral to subhedral dodecahedral or trapezohedral grains which display 6 to 8 sides and as anhedral granular masses |
| Relief RI |
high positive n = 1.675-1.890, highly variable, depending on composition |
Cleavage | none, show irregular fractures |
| Birefringence Interference Colours |
NA NA |
Twinning | not shown |
| Interference Figure Optic Sign 2V |
isotropic - no interference figure | Optic Orientation | NA |
| Composition | highly variable | Alteration | alters to chlorite, commonly involved in a variety of mineral reactions in a variety of metamorphic rocks |
| Occurrence | found in metamorphic rocks of a wide range of compositions, in some Al-rich granitic rocks and as a detritial mineral in sediments | Distinguishing Features | isotropic character, high relief, and grain shape |
