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Rhyodacite – Volcanic rock rich in silica and low in alkali metal oxides – A felsic volcanic rock which is intermediate between a rhyolite and a dacite; Rhyolite – Igneous, volcanic rock, of felsic (silica-rich) composition Comendite – Hard, peralkaline igneous rock, a type of light blue grey rhyolite
In some stones, the inclusion of small, white, radially clustered crystals (spherulites) of the mineral cristobalite in the black glass produce a blotchy or snowflake pattern (snowflake obsidian). Obsidian may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being ...
Lapilli – Rock fragments between 2 and 64 mm in diameter, formed from lava droplets or broken volcanic material. Lapilli can accumulate to form volcanic breccia or tuff. Volcanic ash – Fine particles (<2 mm) of pulverized rock, minerals, and glass created during explosive eruptions. Ash can travel long distances, affecting air quality and ...
Gabbro is known in the construction industry by the trade name of black granite. [31] However, gabbro is hard and difficult to work, which limits its use. [32] The term "indigo gabbro" is used as a common name for a mineralogically complex rock type often found in mottled tones of black and lilac-grey.
Carbonado, commonly known as black diamond, is one of the toughest forms of natural diamond. It is an impure, high-density, micro-porous form of polycrystalline diamond consisting of diamond, graphite , and amorphous carbon , with minor crystalline precipitates filling pores and occasional reduced metal inclusions. [ 1 ]
An anthracite pile in Trevorton, Pennsylvania. Anthracite derives from the Greek anthrakítēs (ἀνθρακίτης), literally "coal-like". [9] Other terms which refer to anthracite are black coal, hard coal, stone coal, [10] [11] dark coal, coffee coal, blind coal (in Scotland), [7] Kilkenny coal (in Ireland), [10] crow coal or craw coal, and black diamond.
Purple was the colour of royalty, and the Roman "imperial porphyry" was a deep purple igneous rock with large crystals of plagioclase. Some authors claimed the rock was the hardest known in antiquity. [3] Thus porphyry was prized for monuments and building projects in Imperial Rome and thereafter.
Diorite (/ ˈ d aɪ. ə r aɪ t / DY-ə-ryte) [1] [2] is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-silica gabbro and high-silica granite.