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Hardness may be difficult to determine, or may be misleading or meaningless, if a material is a mixture of two or more substances; for example, some sources have assigned a Mohs hardness of 6 or 7 to granite but it is a rock made of several minerals, each with its own Mohs hardness (e.g. topaz-rich granite contains: topaz — Mohs 8, quartz ...
Its hardness is theoretically superior to that of cubic diamond (up to 58% more), according to computational simulations, but natural specimens exhibited somewhat lower hardness through a large range of values (from 7–8 on Mohs hardness scale). The cause is speculated as being due to the samples having been riddled with lattice defects and ...
Anonymous owner [4] Star of India: Sri Lanka 563.4 carats (112.68 g) Star Blue-gray American Museum of Natural History, New York [5] Queen Marie of Romania: Sri Lanka 478.68 carats (95.736 g) Cushion Blue Anonymous owner [6] Logan Sapphire: Sri Lanka 422.99 carats (84.598 g) Cushion Blue National Museum of Natural History, Washington [7] Star ...
Emery mine on Naxos Island Corundite from the Naxos emery deposits. The corundum is blue, or sapphire.Wet slab, 10 cm (3.9 in) wide. Emery, or corundite, is a dark granular rock used to make an abrasive powder.
Chrysoberyl is the third-hardest frequently encountered natural gemstone and lies at 8.5 on the Mohs scale of mineral hardness, between corundum (9) and topaz (8). [ 7 ] An interesting feature of its crystals are the cyclic twins called trillings .
The word prasiolite literally means "scallion green-colored stone" and is derived from Greek πράσον prason meaning "leek" and λίθος lithos meaning "stone". The mineral was given its name due to its green-colored appearance. Natural prasiolite is a very light, translucent green. Darker green quartz is generally the result of ...
in Ca 8 (Al 12 O 24) (WO 4) 2, [9] and as in the similar mineral tugtupite (Na 4 AlBeSi 4 O 12 Cl) (see Haüyne#Sodalite group). There is one cavity around each chloride ion. One chloride is located at the corners of the unit cell, and the other at the centre.
Concretions vary in shape, hardness and size, ranging from objects that require a magnifying lens to be clearly visible [13] to huge bodies three meters in diameter and weighing several thousand pounds. [14] The giant, red concretions occurring in Theodore Roosevelt National Park, in North Dakota, are almost 3 m (9.8 ft) in diameter. [15]