Thursday, 12 August 2010


Feldspars are a group of minerals that constitute around 60% of the rocks on the Earth's crust. The pink and white bits in most granites are feldspars. They are found in igneous, metamorphic and sedimentary rocks and have a complicated triangular composition diagram to confuse students of geology. They are alumino-silicate minerals with a balance of either sodium, calcium or potassium filling slots in the molecular structure. The presence of these last three determine the type of feldspar the mineral is. There are also some rare barium feldspars, the wicked uncle of the family. Nobody talks about barium feldspars. They were even booted out of the triangle diagram for insubordination. There are lots of different sub-groups, and further divisions within those. Maybe you can see why I specialised in palaeontology towards the end of my degree.

So far, so what, right? Well, some of these many minerals can be very pretty... See how I bring it down to my level? Bottom left here is moonstone, which is a variety of orthoclase. Up to the right is the colourful labradorite, from the plagioclase group. Sunstone is an oligoclase variety which has tiny plates of hematite that give it a golden shimmer. Amazonite is a pretty green microcline and there are gem varieties of 'normal' orthoclase and albite. I suppose the point is that - brain-eroding chemical shenanigans aside - feldspars are a big group of the most common minerals on the surface of the planet. You'd think they'd be pretty drab, dull things with an inferiority complex. Most of them are, I suppose, but they also have their gems. Even the most ordinary minerals can be beautiful. It's like the ugly duckling or something, isn't it? Don't cry now.