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Hajar | profile | all galleries >> Mineral Galleries >> Crystal Twins >> Twins of Trigonal Minerals >> Calcite Twins tree view | thumbnails | slideshow

Calcite Twins

Calcite (Calcium carbonate) is a very common mineral, but fascinating in the vast variety of crystal forms it assumes, including some beautiful symmetries produced by the phenomenon of crystal twinning ( ).

Four distinct classes of calcite twin have long been recognized, depending on the orientation of the c-axis of each member of the crystal twin relative to the other and the orientation of the twin contact plane. In addition to these cases where adjacent twin members meet at a composition surface approximating a plane, penetration twins also occur (illustrated by examples from Kazakhstan below).

Click on the first image below for a summary of the four twin laws.
Four classes of calcite twins. Drawings of calcite twins in Dana. Dolomite flanged twin, 37 mm. Weisser Fluh, Binntal, Wallis, Switzerland. 8 cm flanged calcite twin from Santa Eulalia, Mun. de Aquiles Serdan, Chihuahua, Mexico. Siderite flanged twin, 18 mm, Mont St Hilaire, Quebec
Calcite twins (twin plane {00.1}) on matrix. Elmwood, Tennessee, USA. 60 and 65 mm on 26 cm matrix. Calcite twin, (twin plane {00.1}), 37 mm, New Street Quarry, Paterson, Passaic County, New Jersey, USA. Gemmy lustrous calcite twin ({00.1}). 1450 Level, Meikle Mine, Bootstrap District, near Carlin, Elko County, Nevada, USA. 3 cm. Twinned calcite crystal (17mm) from Landelies, Belgium shows selectively coated scalenohedral faces from an earlier growth stage Calcite twin (twin plane {00.1}). Cromhall Quartzite Quarry, Gloucestershire, England, UK. 39 mm long.
Calcite twin, (twin plane {00.1}), 26 mm. Hollandtwine Mine, Dirtlow Rake, Castleton, Derbyshire, UK. Calcite twin, Dalnegorsk. Twin plane {01.8}. Calcite twins on matrix. Ocotillo, Imperial County, California, USA. Twins to 14 mm on 3 cm matrix. Twin plane {01.8}. Calcite twin, Pampa Blanca Mine, Huancavelica, Peru. Twin plane {01.8}. Gem calcite twin, Wuzhou, China. Twin plane {01.8}.
30 mm calcite twin ({01.8}), Elmwood Mine, Tennessee, USA Twin plane {10.4}. An immense sharp calcite twin, 13 cm, Verchniy Mine (Verchny Rudnik Mine), Dalnegorsk, Russia. Twin plane {10.4}. Another immense calcite twin, 145 mm, Dalnegorsk, Russia. Twin plane {10.4}. Garden of calcite twin, longest measures 2 cm, Mine No. 884, Leiping, Guiyang, Hunan, China. Twin plane {10.4}.
Huanggang calcite twin, Guanggang, China. Twin plane {10.4}. Calcite twin, 16 mm, Torr Works Quarry (Merehead Quarry), Cranmore, Somerset, England, UK. Calcite, rare axehead twin, 4 cm. Bonsal Moor, Derbyshire, UK. 1981 find.(twin plane {01.2}) Calcite penetration twin, 5 cm gem, Sokolovskoe Iron Mine (Sokolovskiy Mine; Sokol'noye Mine), Kostanay Province, Kazakhstan. Calcite penetration twin, 6 cm gem, Sokolovskoe Iron Mine (Sokolovskiy Mine; Sokol'noye Mine), Kostanay Province, Kazakhstan.
Elmwood calcite twin.jpg DSC00894.jpgTwinned crystals of tabular rhodochrosite to 11 mm on edge, Mont Saint Hilaire, Quebec, Canada