Astrophyllite is one mineral that certainly lives up to its name. “Astrophyllite” is a combination of the Greek words astron (star) and phyllon (leaf). Its shiny bronze-to-gold-colored crystals oft en radiate out as blades from a common center in stellate (starlike) patterns. Against the light-colored matrix in which it is usually found, it looks like a glorious starburst of gold leaf. By contrast, on a streak plate, those metallically bright crystals leave a rather dull and pale greenish-brown streak.
Technically speaking, astrophyllite is a hydrous sodium-potassium iron manganese titanium silicate. Whew, that’s quite a mouthful. It exhibits micaceous cleavage, meaning that it splits apart in thin, brittle leaves, much like a book of common mica. Unlike common mica, astrophyllite is very rare. It grows within rather coarse-grained igneous rocks such as nepheline syenites and alkali granites (also sometimes called “plutonic rocks”) alongside quartz, feldspar, mica, zircon, aegirine, and other minerals.