Description
The mineral astrophyllite is a potassium-sodium-iron-manganese-titanium silicate with the chemical formula K2Na(Fe2+,Mn)7Ti2Si8O26(OH)4. It belongs to the inosilicate family. Golden-yellow, bronze-yellow, or brown to brownish-red astrophyllite has a diamond-like to pearlescent luster, a yellow-brown streak color, and perfect cleavage along the [001] crystal plane. Its average density is 3.34 and its hardness is 3 to 3.5. The crystal system is triclinic, and the mineral's radioactivity is barely measurable. Its gamma ray value, according to the American Petroleum Institute, is 85.21. The name of the mineral astrophyllite is derived from the Greek words astro ("star") and phylon ("leaf"). The mineral astrophyllite occurs primarily in zirconium-bearing syenites. The type locality is the Langesundfjord, near Brevik, Norway.
