A Mystery Solved

Day 334: The human being is by nature a collector, transporting objects from one location to another, there to confound archaeologists ten thousand years down the line. A trove of seashells known only to occur in Polynesia will surface in the center of what is now Kansas someday, and bones from foxes and wolverines may find their way to New Zealand or an East Indian shore. We pick things up and take them home because they're pretty or unusual, or sometimes simply because they appeal to us in some mysterious way. Thus it was that this two-pound hunk of rock managed to creep inside my backpack thirty years ago, and thence to a shelf in my home where it remained a mystery. It was unusual in its original location (perhaps relocated there by another collecting creature like me), a unique find no rockhound could pass by. Thirty years its composition remained a mystery until I met USGS geologist Tom Sisson, who offered to put a sample through testing in order to assuage my curiosity.

Diaspore falls among the minerals referred to generically as bauxite. I quote the authority: "It's diaspore: AlO(OH). I analyzed for Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, Cl, F, S, Sr, and Ba. All I came up with were Al and a little F. The analytical totals were quite low and the mineral damages under the electron beam, which is typical of hydroxides that form at low temperature (we can't analyze for O or H easily). Since the only cation of abundance is Al (excluding possible H), it must be gibbsite (Al(OH)3), diaspore (AlO(OH)), or boehmite (also AlO(OH) but different structure). It's too hard and the habit is wrong for gibbsite or boehmite, but both are right for diaspore."

Believe it or not, I have a couple of people waiting in the wings to hear the result of this analysis. The rock has been returned to my bedroom windowsill where now when my eye falls upon it, I can say, "Diaspore!" and feel richer for knowing.