Agates From Around The World

Day 102: While my husband and I were both rockhounds, his interest was primarily in faceting and lost-wax casting while I leaned more toward the traditional cabochon-cutting and mineral collecting. We both exhibited at gem shows locally, and frequently gave demonstrations in the art of turning rough rock into finished stones. For display purposes, I created a series of 20 x 30 mm. cabochons of agates from sources around the world. Many of these stones came from locations in Washington; some were ones we collected ourselves. Others represent global sources which have now dried up, and good examples of raw materials such as Parrot-wing and Laguna are now very difficult to find.

For the curious among you, I'll post the varieties shown here.
Top row: Blue lace, Scenic, Royal blue, Crazy lace, Cathedral, Tree, Montana
Row 2: Sunset (v. 1), Calico, Graveyard Point plume (backed), Flame, Purple lace, Green moss, Carnelian
Row 3: India moss, Buckskin, Tube, Sagenite, Anderson Dam, Sea-foam chrysoprase, Fortification
Row 4: Parrot-wing, Chalcedony, Utah, Sunset (v. 2), Mount Rainier plume, Yellow moss, Citron chrysoprase
Row 5: Dendritic, Carnelian, Horse Heaven, Banded with pyrite inclusions, Laguna, Arizona flower, Powell Butte moss

Stibnite

Day 101: This is a long walk from the realm of Botany, but I've had another relapse and am getting desperate for bloggable material. That said, I've been interested in other sciences off and on since I was a very small child, and geology/mineralogy filled much of my teenage years. I was forever bringing home pocketsful of rocks (an improvement on tent caterpillars, I suppose), and over the course of time, found a number of examples of unusual native materials including several zeolites. However, true to my nature as a Crow, I longed after other shiny objects, and by the time I was in my early 20s, I'd begun a collection of quality thumbnail specimens. A rockhounding friend had an enormous museum-grade stibnite cluster over which I drooled every time I was in her shop. Eventually, I found a stibnite I could afford (according to the price tag, it cost me all of $5). It has remained one of my most prized specimens despite competition from more brightly coloured and showier pieces. It came from Czechoslovakia. Stibnite is a relatively soft (2.0 Mohs) metallic sulfide (Sb₂S₃) and occurs in long prismatic crystals.

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.