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May-June 2012

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Connoisseur's Choice: Siderite, Siete Suyos Mine, Atocha-Quechisla District Sud Chichas Province, Potosí Department, Bolivia

One of the perks of my job is being able to discuss collecting interests with a wide range of collectors—beginner, intermediate, and advanced. Invariably these conversations turn to the subject of likes and dislikes of the collector, as well as future acquisitions the collector plans to make based upon these likes and dislikes. I have noted from these conversations that just as there is an “A-List” of Hollywood actors and actresses, there is an A-List of mineral specimen likes and desires. At the heading of this list for many collectors is elbaite, a member of the tourmaline group that presents a dazzling array of colors and an equally varied array of habits and associations. Other A-List species include azurite, pyromorphite, fluorite, quartz, and calcite. Then there are the minerals that collectors have less interest in—let's call them “B-List” minerals. The reasons for this are as varied as the species on this list. For instance, I know of one prominent dealer whose adversity to pyrite extends to his not offering any pyrite specimens for sale, and the reason is that he just does not like pyrite. I admit to a bias against most borates, but, in all fairness, this has more to do with the extreme humidity levels of the Washington, D.C., area, which can cause fine borax crystals to become detergent powder, than any general dislike for those particular species. Through these discussions with collectors, I began making a list of minerals that make no one's A-List. These are the minerals that, to continue on with the Hollywood analogy, are superb character actors but lack the charisma to be a star actor or actress for one reason or another. At the top of this list I have to put micas—great as associated minerals in a pegmatite situation but rarely a star. A mineral I always considered a B-List member, one that makes superb backgrounds for the A-List minerals, is siderite. Its typical brown color is perfect for highlighting stars from galena and ferberite right up to colorful fluorapatites. However, while going through the reference collection drawers here in the museum recently, I have come to realize that, like muscovite (which I will feature at a later time), siderite is an underappreciated star in its own right.

Paul W. Pohwat is the collections manager (minerals) in the Division of Mineralogy at the National Museum of Natural History.

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