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Identify metamorphic rock; properties of sandstone and granite

Short answer

Metamorphic rocks show foliation, slaty cleavage, crystalline sugary texture, typical minerals (garnet, mica), and distorted structures. Sandstone: clastic, quartz grains, porous, strength 20–170 MPa depending on cement. Granite: coarse crystalline, quartz/feldspar, specific gravity2.6–2.8, strength100–250 MPa.

How do you identify a metamorphic rock in the field? Describe the physical properties of sandstone and granite.

Identifying a metamorphic rock in the field

  1. Foliation: parallel alignment of minerals, banding or schistosity (slate, phyllite, schist, gneiss).
  2. Slaty cleavage: splits into thin, hard slabs.
  3. Crystalline, sugary texture (marble, quartzite), with no layers or fossils.
  4. Typical minerals: garnet, kyanite, chlorite, mica, staurolite, talc.
  5. Distorted structures: folds, crumpled bands, stretched pebbles.
  6. Often hard, dense and found in mountain belts or near intrusions.

Physical properties of sandstone

  • Sedimentary, clastic rock of sand-sized grains (mostly quartz) cemented by silica, calcite or iron oxide.
  • Colour: white, yellow, red, brown or grey; bedded; granular texture, gritty feel.
  • Specific gravity 2.2-2.7; porosity 5-25%; compressive strength 20-170 MPa depending on cement; hardness 6-7 for quartz grains.

Physical properties of granite

  • Igneous, intrusive, coarse-grained, crystalline rock of quartz, feldspar and mica or hornblende.
  • Colour: pink, grey or white, speckled; massive, hard; specific gravity 2.6-2.8; porosity under 1%; compressive strength 100-250 MPa; takes high polish.

✓ Answer checked by Claude Opus 5.5 (high effort)

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