Rhodonite
Disdaining ecology and parentage, some minerals always look the same: gold, silver, pyrite, realgar, malachite, and azurite, to name a few, are always easy to spot for what they are. Other minerals, possibly more sensitive to temperature, pressure, acidity, and solution concentration as they form, may look very different depending on where they grew and can be difficult to identify properly. Rhodonite belongs in this group.
In some incarnations, rhodonite, a manganese mineral, is a rich-pink to rose-colored massive material, such as the historic occurrence in Sverdlovsk, Russia. Impressive rhodonite carvings were perhaps the second choice of the Czars as wedding presents with which they burdened many of the royal families of Europe, the first choice being giant urns and tables covered with a mosaic of stunning green malachite, also mined in Russia. Among the choicer products of the famous Ekaterinburg lapidary shops that turned out items for the Czars were rich-red plates of solid, massive rhodonite.
The Sverdlovsk rhodonite results from the meta-morphism of sedimentary formations rich in manganese oxide, in response to subsurface thermal conditions, including the introduction of silica. Under these conditions, the manganese loses its typical, very black appearance and the rhodonite becomes instead a maelstrom of interlocking red crystals — practically a rock, and of use in carvings. There are a good many such massive rhodonite formations in the world, and although comparable super lapidary quality rhodonite seems to be rare, the cutters of Germany’s Idar-Oberstein still seem able to obtain enough rough. With many older localities reopening, we have probably already seen fresh material from the historic Russian source.
If it isn’t by now under some real estate development, there is or was such a similar occurrence near Plainfield, Massachusetts. On exposure to weathering, many manganese minerals oxidize quickly, seeming to get very black almost overnight. This makes collecting them in the field good exercise: until a hammer creates a fresh surface on every boulder, it’s impossible to be sure what mineral lies within. An additional complication is that manganese oxide stains seem to get on everything even near a manganese-rich formation, blackening every rock within yards of the outcrops and staining alike cumming-tonite, garnet, and quartz.
Under open-pocket conditions, rhodonite usually develops a habit that is very typical of triclinic minerals: sharp, spear-point wedges, such as those found in the Chiurca mine in the Huallanca Province of Peru. Bright and fresh, some of these specimens are the most spectacular examples of this type of rhodonite. Brazil’s Minas Gerais also has a vein occurrence of these crystals near the hematite mining area, and while they look promising, they haven’t as yet lived up to their billing. Small numbers of specimens of the vein type were also found Langban, Sweden, and in several Japanese mines.
Sometimes in addition to rhodonite, nature gives us a “friend”: a mineral similar in some ways but a distinct species. Pyroxmangite is one friend frequently associated with rhodonite, found in some of the Japanese occurrences, for instance, and is often confused with it. Bustamite, the other friend, contains considerable calcium and possibly forms an isomorphous series with rhodonite (which can accept some calcium without materially changing its nature). Rhodochrosite sometimes accompanies rhodonite, but not at the major occurrences.
In New Jersey, a complex geologic history saw solutions with additional elements invading the famed Franklin, New Jersey, occurrence, and recrystallization veins developed with small open pockets. Crisscrossing this speckled mixture, rhodonite crystals exhibit the saw-tooth habit characteristic of unhampered vein growth. Also found there is willemite in yellow to greenish gemmy prisms, accompanied by yellow manganaxinite, brown spessartine garnets, and the rarities such as hodgkinsonite, cahnite, friedelite, and the like.
Rhodonite is a major Franklin species, with specimens unlike rhodonite from anywhere else: opaque, pink, equant or shoebox crystals two to three inches long, embedded in red-fluorescing calcite. The like or equant dimensions suggest that when rhodonite crystals grow under hydrostatic pressure, like more plentiful garnets and andalusite in a similar pressure environment, their shape is quite unlike that of the spiky rhodonites found in pockets within veins. The typical old-time rhodonite specimen of a Franklin collector consisted of two- or three-inch, interlocking opaque pink crystals that had been carefully worked out of a coarsely crystalline (and red fluorescing) calcite matrix, accompanied by black franklinite octahedra, orangey-brown manganiferous willemite (called troostite) and rounded blebs of red zincite.
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