UNIT II
MEGASCOPIC IDENTIFICATION OF ROCKS
Hand-specimen identification based only on features visible to the naked eye.
Basalt • Dolerite • Granite • Pegmatite • Laterite • Sandstone • Limestone • Conglomerate • Shale • Slate • Phyllite • Schist • Quartzite • Gneiss • Marble
Our Geo | https://ourgeo.online Page 1
1. BASALT
IDENTIFICATION
1. Dark grey to black colour.
2. Very fine-grained appearance; individual crystals are generally not clearly visible to the naked eye. 3. Compact, massive surface with a dull to slightly rough appearance.
4. Small vesicles may be visible on some specimens.
Our Geo | https://ourgeo.online Page 2
2. DOLERITE
IDENTIFICATION
1. Dark grey to black colour.
2. Fine- to medium-grained crystalline appearance.
3. Small light and dark mineral grains can be distinguished with the naked eye. 4. Compact, hard and massive-looking specimen.
Our Geo | https://ourgeo.online Page 3
3. GRANITE
IDENTIFICATION
1. Light grey, pinkish or whitish overall colour with dark mineral specks. 2. Coarse-grained texture; individual mineral grains are clearly visible.
3. Interlocking grains of different colours give a characteristic speckled appearance. 4. Commonly shows white/grey grains, pink grains and black mica-like grains.
Our Geo | https://ourgeo.online Page 4
4. PEGMATITE
IDENTIFICATION
1. Generally light coloured, commonly white, pink or grey.
2. Extremely coarse-grained appearance with unusually large crystals.
3. Large light-coloured crystals are easily visible to the naked eye.
4. Black or silvery mica-like flakes may be conspicuous.
Our Geo | https://ourgeo.online Page 5
5. LATERITE
IDENTIFICATION
1. Reddish-brown to orange-brown colour.
2. Earthy, rough and commonly porous surface.
3. Irregular pits and small cavities may be visible.
4. The specimen commonly has a ferruginous, rusty appearance.
Our Geo | https://ourgeo.online Page 6
6. SANDSTONE
IDENTIFICATION
1. Usually buff, yellowish-brown, reddish or grey in colour.
2. Sand-sized grains are visible as a granular surface.
3. Bedding or thin layers may be visible across the specimen.
4. The surface commonly has a rough, sandy appearance.
Our Geo | https://ourgeo.online Page 7
7. LIMESTONE
IDENTIFICATION
1. Usually white, cream, light grey or pale brown.
2. Fine- to medium-grained appearance.
3. Fossil fragments, small cavities or irregular patches may be visible in some specimens.
4. Generally has a dull, earthy to slightly crystalline surface.
Our Geo | https://ourgeo.online Page 8
8. CONGLOMERATE
IDENTIFICATION
1. Very coarse-grained appearance.
2. Rounded pebbles and cobbles of different colours are clearly visible.
3. Pebbles are enclosed in a finer-grained matrix.
4. The rounded clasts give the specimen a distinctive pebbly appearance.
Our Geo | https://ourgeo.online Page 9
9. SHALE
IDENTIFICATION
1. Usually grey, dark grey, black, brown or reddish.
2. Very fine-grained surface; individual grains are not normally visible.
3. Distinct thin, closely spaced layers are visible.
4. The specimen commonly appears flat, thinly layered and fissile.
Our Geo | https://ourgeo.online Page 10
10. SLATE
IDENTIFICATION
1. Commonly grey, dark grey, greenish or purplish.
2. Very fine-grained and compact appearance.
3. Strong, closely spaced planar cleavage is visible.
4. The specimen commonly forms thin, flat, sheet-like surfaces.
Our Geo | https://ourgeo.online Page 11
11. PHYLLITE
IDENTIFICATION
1. Usually grey, greenish-grey or silvery-grey.
2. Fine-grained foliated appearance.
3. A characteristic silky or satiny sheen is visible on the foliation surfaces.
4. Thin, closely spaced foliation planes can be seen.
Our Geo | https://ourgeo.online Page 12
12. SCHIST
IDENTIFICATION
1. Colour varies, commonly grey, silvery, brown or dark.
2. Medium- to coarse-grained appearance with visible mineral flakes.
3. Strong foliation is clearly visible as parallel mineral alignment.
4. Mica-like flakes commonly give the surface a shiny appearance.
Our Geo | https://ourgeo.online Page 13
13. QUARTZITE
IDENTIFICATION
1. Usually white, grey, pinkish, brown or greenish.
2. Granular and crystalline appearance.
3. Quartz grains appear tightly interlocked; the rock looks massive rather than layered.
4. Fresh surfaces commonly show a hard, glassy to sugary-looking texture.
Our Geo | https://ourgeo.online Page 14
14. GNEISS
IDENTIFICATION
1. Usually shows alternating light and dark bands.
2. Coarse-grained texture with mineral grains visible to the naked eye.
3. Light and dark minerals are arranged in distinct bands or streaks.
4. The specimen commonly has a strongly banded, foliated appearance.
Our Geo | https://ourgeo.online Page 15
15. MARBLE
IDENTIFICATION
1. Commonly white, cream, grey or pinkish, sometimes with coloured veins.
2. Crystalline, granular appearance; calcite grains may be visible.
3. Interlocking crystals give the surface a sugar-like or sparkling appearance.
4. Usually massive and non-foliated, without the strong banding seen in gneiss or schist.
Our Geo | https://ourgeo.online Page 16
কোন মন্তব্য নেই:
একটি মন্তব্য পোস্ট করুন