Provide a detailed rock description. Must include: - Modal minerology (e.g. 35%

Question

Provide a detailed rock description.

Must include:

- Modal minerology (e.g. 35% quartz, 25% plagioclast etc.),

- Detailed description (e.g. Sample X1 is a light-coloured rock, with pinkish K-feldspar crystals. The sample is coarse grained (grainsize range: 2-10 mm), phaneritic, and has a weakly porphyritic texture, with K-feldspar phenocrysts being larger than the other minerals on average. Plagioclase, K-feldspar and biotite exhibit subhedral microstructures, quartz is anhedral. The rock exhibits no obvious metamorphic fabrics (foliation is absent))

- other features

- A Rock name

Explanation / Answer

The given sample is a dark colored, extrusive igneous rock with whitish plagioclase crystals. It consists of 60% mafic minerals (which includes pyroxene mostly), 30% calcic plagioclase feldspar and 10% other crystals. The sample is very fine grained, aphanitic, and has a glassy matrix which is interspersed with visible mineral grains. Plagioclase and pyroxene exhibit subhedral shape whereas quartz is anhedral. The dark colour of the rock is due to the presence of abundant dark colored minerals (pyroxene, hornblendce etc). The rock exhibits no obvious metamorphic fabrics (lineation and foliation is absent) and the hand specimen shows porphyritic texture with visible grains of feldspar. Vesicles are also present in few places which clearly indicates the sample to be basalt.

Rock name : BASALT.

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