Another group of radiate fibrous growths resembling spherulites in many respects consists of minute feathery crystals spreading outwards through a fine grained or glassy rock. In the variolites there are straight or feathery feldspar crystals (usually oligoclase) forming pale colored spherulites a quarter to half an inch in diameter. The same rocks often contain similar aggregates of plumose skeleton crystals of augite. Many volcanic rocks have small lath-shaped crystals of feldspar or augite diverging from a common center.
Read more about this topic: Spherulite
Other articles related to "variolites":
... Other variolites are glassy or partly crystalline facies of olivine-free dolerites, occurring as thin dikes or intrusions or at the margins of dolerite masses ... to a point one example of these rocks from Skye contains variolites over three inches in diameter ... Another group of variolites includes the most famous rock of this type, which comes from the Durance, in France ...