Deformation Twinning in Stibnite from Punjab, India

Prismatic sections of stibnite obtained from-Punjab, India, show various types of twinning, whose nature indicates deformation origin of the twinning . The twinning is simple or repeated or polysynthetic; in the latter case the twin lamellae may be parallel, wedge-, lens- or spindle-shaped, twisted and sinuous.

The disposition of the twinning lamellae and their relation to the (010) cleavage indicate that twin gliding has taken place in the plane (001) along [010]. This is probably due to the least coherence along [010]. The various patterns of twin lamellae are due to (a) trans­ lation gliding (010) [001] (b) bending about [100] and © twisting about [001] subsequent to the twinning. The simple types of twins are either due to accumulation of localised stresses during alteration or due to grinding and polishing, and the complex ones are due to shearing movements during or after deposition of stibnite.