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Mineral Monday: Garnet

A Raw Garnet- Photo by MB Griggs

It’s already January 24, and the return of grad school classes. Unbelievable! This mineral monday we’re going to go sparkly, with January’s birthstone, the garnet. My family loves doing gem mining at roadside stands in the North Carolina mountains, looking for color and sparkling stuff in buckets of grit. It took us several times to figure out that the heavy, round, rough-textured rocks that we kept throwing away were actually large garnets that could be cut into beautiful gems. Garnets tend to have a lovely reddish-orange to red-purple color when cut, as you can see below.

Cut Garnets Photo by: Opacity from Flickr

Garnets are a subgroup of minerals that belong to the nesosilicate group. Nesosilicate refers to the way that molecules are arranged within the mineral structure. All nesosilicates have the same basic structure, with tetrahedra of SiO4 (silicon and oxygen arranged in a tetrahedron) connected by cations. Garnet minerals have this arrangement with most of the basic SiO4 units arranged in groups of three with Magnesium, Aluminum, Calcium, or Chromium acting as the cations. I know… whoa… chemical formulas, but it’s what makes garnets, garnets! They’re very hard minerals, but relatively easy to cut into gem-like shapes- perfect for use in jewelry and decoration.

Garnet Necklace from Houston Museum of Natural Science Photo by sulla55 From Flickr

One Comment

  1. LMG wrote:

    Well done, as usual! Thanks for the chemical formulae–they corrected an assumption on my part that garnets contained iron. I found it easy to believe because of the orange-ish color and the feeling of higher density compared to some other gems. Perhaps it’s just my imagination, though…

    Tuesday, January 25, 2011 at 7:32 pm | Permalink

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