Twinning is common in gypsum crystals which often results in beautiful swallowtail habit.
I saw very nice exposure of swallowtail gypsum crystals in Cyprus. The crystals are several meters long and they all seem to be twinned.
These crystals formed in a shallow hypersaline lagoon in the Messinian (the last stage of the Miocene) about 6 million years ago. I have also written about laminated gypsum that is exposed nearby and formed roughly at the same time but probably in somewhat deeper water.
Twinned gypsum crystals (selenite) in Cyprus near Elediou. I know some of you might be worried about the hammer but I can assure you that I used it for scale only. I always carry it in my backpack when geologising and use it more often for scale (if pen is too small) than for smashing rocks. I would not consider destroying an exposure as beautiful as this and I very rarely attack outcrops at all. However, I do collect and often smash loose rocks.
I am now back home from Cyprus. It was very interesting geotrip and I will definitely use material collected there (sand, rocks, and photos) in many more posts in the future. For some time my posts will remain short because my time is very limited. If I’ll feel the urge to write, I should write my masters thesis instead. However, I do not want to abandon my blog. Maybe not daily but several times a week at least I will post some photos with brief comments.
good luck with that thesis!