What type of rock has really big minerals and lots of uncommon elements? It's a pegmatite! Pegmatites contain lots of important elements and minerals, both for our economy and for mineral collectors.
Join us for a tour of pegmatites. We give quick low-down on how pegmatites form. They contain really large mineral grains, which usually implies that they cooled slowly. But, pegmatites form from the leftover fluids from magma chambers and contain all the uncommon (or unpopular!) elements that get concentrated. Once they reach a certain concentration they form rare minerals that are concentrated in things like Lithium, Cesium, or Beryllium!
The minerals in pegmatites grow so fast because the fluid they grow in is much less viscous (more watery) than magma. This means that atoms and ions can diffuse much more quickly to the sites of mineral nucleation, allowing for massive (really really massive, up to 30 ft) crystals of minerals like spodumene and beryl to form.
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