Twins in cryolite types from Ivigtut, South Greenland

• Main Authors: Hans Pauly, Twl Tp
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1978
• Subjects: Greenland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.497.7543; http://2dgf.dk/xpdf/bull27-noe-nygaard-7-14.pdf

The appearance of twins in various coarse grained types of cryolite from Ivigtut is illustrated. The examina-tion is based on large thin sections (from 5 cm to 12 cm across) of pure, white large-grained cryolite, similar large-grained cryolite from fluorspar-cryolite and from a vein of pure, black cryolite in the wallrocks. The seven twin laws identified by Bøggild (1911, 1912) were found in most samples. The sample from fluorite-cryolite was dominated by the twin law (001) and the sample from the vein was dominated by [021]l2°. The general picture seems to favour a mechanical formation of all twins in the samples. The characteristic parting of cryolite is intimately related to the presence of twin lamellae, mainly as reported by Bøggild (1911, 1912), corresponding to the law [021]'20 but also (110) (Bøggild 1913), and (001) as observed in the sample from fluorite-cryolite here examined. This sample also contains indications for several stages of reorienta-tion presumably in response to outside stress situations.