Homework answers / question archive / Rock 1 Very fine grained (0

Rock 1 Very fine grained (0

Sociology

Share With

Rock 1 Very fine grained (0.5 mm size crystals), aphanitic, vesicular, melanocratic to mesocratic basalt (scoria), consisting of mixture of plagioclase and pyroxene in approximately 50%-50% proportion. Rock 2 Fine grained, porphyritic, melanocratic basalt. Phenocrysts of plagioclase (elongated, up to 1 cm, transparent crystals) and pyroxene (black crystals, up to 1 cm in size). Phenocrysts constitute about 10 % of the rock. Ground mass is black in colour and made of 50:50 mix of plagioclase and pyroxene grains (less than 0.5 mm in size) Rock 3 Fine grained, aphanitic, leucocratic rhyolite. Grains (less than 0.5 mm in size) of two minerals appear to be present in 50:50 proportion. One is white in colour, another is greyish to brownish. It is difficult to determine precisely what minerals they represent. Rock 3 Porphyritic, mesocratic andesite. Phenocrysts 0.5 to 1 cm large, zoned feldspar (about 40%). Groundmass dark-brown aphanitic (about 60%) Rock 5 Fine grained, aphanitic, vesicular, leucocratic rhyolite (pumice). Crystals probably representing two different minerals (one white and other light grey to transparent) less than 0.5mm in size. Rock 6 Coarse grained, melanocratic, equigranular peridotite (strictly speaking pyroxenite). Green pyroxene grains between 0.5 and 1 cm in size (about 90-95%) and white to light grey crystals of feldspar (510%) Rock 7 Coarse grained (3 to 8 mm grains), equigranular, leucocratic to mesocratic granite. Mineral composition: Feldspar (white to light grey grains, ~60%), quartz (dark grey, transparent grains, ~30%) and biotite (black grains, ~10%) Rock 8 Coarse grained, leucocratic equigranular diorite. Mineral composition: Feldspar (white grains up to 1 cm in size, 60-70%), amphibole (black elongated grains with length also up to 1 cm, 40-30%) Rock 9 Coarse grained, mesocratic to melanocratic, equigranular gabbro. Mineral composition: Feldspar (white grains 3-5mm in size, 50%), pyroxene (black short prismatic grains 3-5mm in size, 50%) Rock 10 Very fine grained (significantly less than 1mm clasts), dark grey, well sorted, finely laminated (submm layers) mudstone (shale). Formed in low energy environment (lagoons, lakes etc.) Rock 11 Fine to coarse grained, yellow with brown staining, poorly sorted (subrounded quartz clasts range in size from 1 to 2 mm) sandstone. Formed in medium energy environment (e.g. river channels). Clasts ~90%, cement (white) ~10%. Rock 12 Cream to brownish, shell fragment-rich limestone. Reacts with diluted HCl. Shell fragments close to 70-80% of the rock and range in size from a few mm to 2 cm. The rest is cement (white). Formed at the shelf. Broken shell fragments indicate high energy environment, near beach with strong waves. Rock 13 Brown, laminated (thickness of lightly coloured silica rich layers and darker iron oxide rich layers is about 1 cm) banded iron formation (BIF). Formed at ocean floor. Rock 14 Medium to very coarse grained, poorly sorted conglomerate. Clasts 1-2 cm in size rounded, about 30%. Matrix 1-3 mm in size sub-angular grains, about 50%. Cement (white) about 20%. Formed in a high energy environment (e.g. alluvial fan) Rock 15 Green to red unevenly coloured, glassy, chert. Uneven (conhoidal) surface. Formed in deep sea environment. Rock 16 Light yellowish grey, medium grained (2 mm crystals) quartzite. Medium grade of metamorphism (based on grain size). Parent rock –sandstone. Rock 17 Granular, black, medium grained (1-2 mm black pyroxene grains) granulite with porphyroblasts of garnet (red) up to 1 cm in size. Parent –basalt, High grade of metamorphism (granulite facies) Rock 18 Medium grained (2 mm) amphibolite. Amphibole (black) shows pronounced lineation and is about 50% of the rock. Feldspar (white) also shows preferred orientation. Metamorphic grade medium (amphibolite facies). Parent - basalt Rock 19 Medium grained biotite or amphibole (black), garnet (red) gneiss. Gneissic banding with the bands 0.5-1 cm thick. Grade of metamorphism – high. Parent – mudstone. Rock 20 Medium grained (1-2mm), greenish, foliated (schistosity) chlorite schist. Grade of metamorphism – low. Parent – basalt Rock 21 Granular, fine grained (less than 1mm), white marble. Reacts with diluted HCl. Grade of metamorphism low (based on the grain size). Parent rock – limestone Rock 22 Strongly foliated (schistosity), medium grained (1-2mm), biotite schist. Grade of metamorphism medium. Parent – mudstone Rock 23 Very fine grained (less than 1 mm), foliated (slaty cleavage), dark green to black slate. Grade of metamorphism – low. Parent - mudstone