Chain silicate
Crystal system: monoclinic (+)
Colour in hand specimen: black
Cleavage: two at 90°
Hardness: 5.5-6
Colour in plane polarised light: colourless, pale brown or pale grey
Pleochroism: variable weak to moderate
Relief: moderate
Birefringence: 0.018-0.033; 1st order pink to 2nd order orange
Extinction: inclined
Twinning: simple, common
Clinopyroxene contains calcium. It encompasses a range of solid solutions from (Mg,Fe)2[Si2O6] to Ca(Mg,Fe)[Si2O6]. The physical and optical properties detailed above refer to augite, a clinopyroxene common in mafic igneous rocks.
Chain silicate
Crystal system: monoclinic (+)
Colour in hand specimen: black
Cleavage: two at 90°
Hardness: 5.5-6
Colour in plane polarised light: colourless, pale brown or pale grey
Pleochroism: variable weak to moderate
Relief: moderate
Birefringence: 0.018-0.033; 1st order pink to 2nd order orange
Extinction: inclined
Twinning: simple, common
Clinopyroxene contains calcium. It encompasses a range of solid solutions from (Mg,Fe)2[Si2O6] to Ca(Mg,Fe)[Si2O6]. The physical and optical properties detailed above refer to augite, a clinopyroxene common in mafic igneous rocks.
Olivine
- Subhedral to euhedral grains making up ~45% of the rock. Alteration to magnetite and serpentine, particularly along the curving cracks. Cracks across the thin-section, could be due to expansion of the rock as the olivine was altered.
Clinopyroxene
- Interstitial phase making up ~35% of the rock. Moderate relief, inclined extinction and first order pink to second order orange interference colours.
Plagioclase feldspar
- Interstitial phase making up ~20% of the rock. Low first order interference colours and lamellar twinning.
Accessory minerals - Biotite, small, interstitial grains, altered.
This is a cumulate rock. It has undergone late-stage shear banding.
Olivine phenocrysts crystallised first.
Clinopyroxene grew around the olivine phenocrysts.
Interstitial feldspar filled in the remaining gaps.
Shearing of the rock produced bands of deformation.
Hydrothermal alteration.
Olivine
- Subhedral to euhedral grains making up ~45% of the rock. Alteration to magnetite and serpentine, particularly along the curving cracks. Cracks across the thin-section, could be due to expansion of the rock as the olivine was altered.
Clinopyroxene
- Interstitial phase making up ~35% of the rock. Moderate relief, inclined extinction and first order pink to second order orange interference colours.
Plagioclase feldspar
- Interstitial phase making up ~20% of the rock. Low first order interference colours and lamellar twinning.
Accessory minerals - Biotite, small, interstitial grains, altered.
This is a cumulate rock. It has undergone late-stage shear banding.
Olivine phenocrysts crystallised first.
Clinopyroxene grew around the olivine phenocrysts.
Interstitial feldspar filled in the remaining gaps.
Shearing of the rock produced bands of deformation.
Hydrothermal alteration.