Like labradorite it usually exhibits on the surface of easiest cleavage parallel striations due to twinning structure.
In families where twinning is frequent, bodily deformities likewise occur with frequency.
But by far the most important kind of regular conjunction of crystals is that known as “twinning.”
The plate of material is rather wider than before, and is formed into two combs simultaneously, by the aid of a twinning machine.
The second method, known as “twinning” or “parting,” avoids this loss and is also more rapid.
It is of some interest on account of the twinning and the beautiful development of its crystals.
This twinning may be produced by pressure acting either during the crystallization of the rock or at a later period.
A twinning line, if an intersection edge, should be solid; if not an intersection edge it should be broken into dashes.
Old English twinn "consisting of two, twofold, double," probably ultimately from Proto-Germanic *twinjaz (cf. Old Norse tvinnr, Old Danish tvinling, Dutch tweeling, German zwillung), from PIE *dwisno- (cf. Latin bini "two each," Lithuanian dvynu "twins"), from *dwi- "double," from root *dwo- "two" (see two). The verb meaning "to combine two things closely" is recorded from late 14c. The noun developed from Old English getwinn "double."
twinning twin·ning (twĭn'ĭng)
The bearing of twins.
A pairing or union of two similar or identical objects.
One of two offspring born at the same birth. adj.
Being two or one of two offspring born at the same birth.
Consisting of two identical or similar parts; double.