The Sterling and Franklin Mines are co-type localities for zincite. The mineral was very abundant here. But not as crystals. Even micro crystals are rare.
These crystals are very small, but they are remarkable in one respect – they are bi-pyramidal! Zincite is hemimorphic and the almost universal habit of natural crystals is a hexagonal pyramid. The pyramids can be very steep or quite shallow, and various combinations occur. Tabular crystals also occur, but these are extremely rare. But the pyramidal crystals are almost always “one-sided”.
As can be seen in the first photo, some of the crystals on this specimen are decidedly “two-sided”, albeit the development is asymmetric – as befits the hemimorphism of zincite. Please note that FOV in the first photo is only 1.1 x 0.9 mm and the center crystal is only about 0.4 mm “tall” by 0.4 mm wide. Such tiny things are really beyond the capabilities of my equipment. The original photo suffered from truly “world class” chromatic aberration and I had to do unspeakable things to make the photo presentable. But I chose to show this crystal first because it is the clearest example of the bi-pyramidal habit. You will need 30-60X to view it. (At very high magnification, it appears that the “other” pyramid is really a tapering stack of basal plates – there seem to be no actual pyramidal faces.)
The largest crystal is about 0.6 mm wide by 0.5 mm tall. It is shown at top right in the next pair of photos and bottom left in the following two pairs of photos (FOV 2.0 x 2.5 mm and 2.2 x 2.9 mm resp.). This crystal is bi-pyramidal, but not obviously so. Some of the smaller crystals in these photos are, however, clearly bi-pyramidal.
In addition to the deep orange di-pyramids, the yellow radiating acicular – almost fibrous – stuff is also zincite.
But that’s not all. This specimen also has some tiny, but very sharp crystals of pyroaurite – a very rare mineral at the Sterling Mine. Some of the pyroaurite is shown in the last micro photo. FOV is just 1.6 x 0.9 mm. The hexagonal crystal on the left is 0.2 mm in diameter, the crystal seen edge-on on the right is a bit bigger – paehaps 1/4 mm. At this scale, nothing is very sharp in the photo. Things will look sharper in a scope. But you will need 50-60X.
Small as they are, some of the zincite crystals are visible in the macro photo. The matrix is “salmon” calcite with a few blebs of franklinite and willemite. Only the willemite fluoresces.
Bottom line: This is a very small specimen, with tiny – but remarkable – crystals.
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