Where This Rock Is From (place, type of locality, etc.)
The parent of one of my students works at a business that makes "granite" countertops and vanities. When the student found out about my interest in rocks, he brought me a bucket full of cut leftovers from the workshop. This rock caught my eye because of the unusual color and texture.
What This Rock Is
This rock is a medium grained sodalite syenite. It is almost entirely composed of alkali feldspar (white and occasionally pink) and sodalite (bright blue). It contains no quartz but may have small amounts of hornblende, pyroxene, and biotite. Other names for this rock are foyaite and foid syenite. These rocks are rare and occur in small igneous intrusions. This particular variety comes from Bahia, Brazil and is nicknamed AZUL BAHIA in the trade. Besides decorative uses, this rock is mined for the sodalite which is used in manufacturing ceramics.
What I Like About This Rock
The bright blue crystals of sodalite blew me away! When I first saw this piece, I thought it was a manufactured product because blue rocks are so rare in nature. I pulled out all of my rock reference books and began searching for answers. Identifying an unknown rock is always an enjoyable challenge.
Advice
- I've discovered that most dimensional and decorative stone that is called granite is not actually granite. I found a great web site that showed photos of the rocks and listed their actual name, trade name, and origin. The internet is a great resource for rock identification.
Andrew Alden, Geology Guide, says:
Nearly all blue rocks are metamorphic, but the rare silica-deficient feldspathoid rocks are an exception in the igneous family. A nice specimen to launch this collection!I feature some material on commercial stone names here.
