ROCKS

Listing description Basalt is a common extrusive igneous ( volcanic ) rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. By definition , basalt must be an aphanitic igneous rock with less than 20% quartz and less than 10% feldspathoid by volume, and where at least 65% of the feldspar is in the form of plagioclase . Basalt is usually grey to black in colour , but rapidly weathers to brown or rust-red due to oxidation of its mafic (iron-rich) minerals into rust . Detailed description It almost always has a fine-grained mineral texture due to the molten rock cooling too quickly for large mineral crystals to grow, although it can sometimes be porphyritic , containing the larger crystals formed prior to the extrusion that brought the lava to the surface, embedded in a finer-grained matrix . Basalt with a vesicular or frothy texture is called scoria , and forms when dissolved gases are forced out of solution and for...

Listing description Blueschist / ˈ b l uː ʃ ɪ s t / , also called glaucophane schist, is a metavolcanic rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures , approximately corresponding to a depth of 15 to 30 kilometers and 200 to ~500 degrees Celsius. The blue color of the rock comes from the presence of the predominant minerals glaucophane and lawsonite . Detailed description Blueschists are typically found within orogenic belts as terranes of lithology in faulted contact with greenschist or rarely eclogite facies rocks. Petrology Blueschist , as a rock type, is defined by the presence of the minerals glaucophane + ( lawsonite or epidote ) +/- jadeite +/- albite or chlorite +/- garnet +/- muscovite in a rock of roughly basaltic composition. Blueschist often has a lepidoblastic , nematoblastic or schistose rock microstructure defined primarily by chlorite, phengitic white mica , glaucop...