Twinning
Barium feldspars occur in optically uniform crystals where the twinning is poorly developed, except on coarse crystals. Eighteen crystal forms have been identified; eleven of them coincide with those known for orthoclase. Observed twining includes manebach twins on (001) and baveno twins on (021). Some samples of celsian were found to have a rare lamellar twinning (Spencer, 1941).
Read more about this topic: Celsian