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Blueschist on Île de Groix, France Photomicrograph of a thin section of blueschist facies metamorphosed basalt, from Sivrihisar, Turkey. Blueschist (/ ˈ b l uː ʃ ɪ s t /), also called glaucophane schist, is a metavolcanic rock [1] that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures (200–500 °C (392–932 °F ...
Llanite is a porphyritic rhyolite with distinctive phenocrysts of blue quartz (a rare quartz color) and perthitic feldspar (light grayish-orangeish). The brown, fine-grained groundmass consists of very small quartz, feldspar, and biotite mica crystals.
Quartzite is a very hard rock composed predominantly of an interlocking mosaic of quartz crystals. The grainy, sandpaper-like surface is glassy in appearance. Minor amounts of former cementing materials, iron oxide, silica, carbonate and clay, often migrate during recrystallization, causing streaks and lenses to form within the quartzite. [ 1 ]
Substitution of iron and other tri-valent elements for aluminium result in the color variations. It has a Mohs hardness of 7 and a specific gravity of 3.3 to 3.4. Crystals show pleochroism from red to blue to violet. Dumortierite quartz is blue colored quartz containing abundant dumortierite inclusions.
The most common color of aventurine is green, but it can also be orange, brown, yellow, blue, or grey. Chrome-bearing fuchsite (a variety of muscovite mica) is the classic inclusion and gives a silvery green or blue sheen. Oranges and browns are attributed to hematite or goethite.
Blue Granite – Variety of monzonite, an igneous rock; Epidosite – Hydrothermally altered epidote- and quartz-bearing rock; Felsite – Very fine-grained volcanic rock that sometimes contains larger crystals; Flint – Cryptocrystalline form of the mineral quartz; Ganister – Hard, fine-grained quartzose sandstone, or orthoquartzite
Color is generally white through light gray, or red to tan and may include any color except dark gray, green or black (the colors of trap rock). [1] The mass of the rock consists of a fine-grained matrix of felsic materials, particularly quartz , plagioclase and potassium feldspar , [ 2 ] and may be termed a quartz felsite or quartz porphyry if ...
Quartz crystal with chlorite inclusions from Minas Gerais, Brazil (size: 4.2 × 3.9 × 3.3 cm) Chlorite is a common mineral, found in metamorphic, igneous, and sedimentary rocks. It is an important rock-forming mineral in low- to medium-grade metamorphic rock formed by metamorphism of mafic or pelitic rock. [9]