amnhnyc:

Have you ever wondered how big crystals form? Let’s talk about it this #MineralMonday.💎

Pegmatites produce large crystals—usually over ~1⁄2 inch (1 cm)—and are the final product of some cooling magmas. They’re found in veins, dikes, or pods at or near the margins of large igneous bodies. Large crystals and distinctive textures can form in pegmatites because high concentrations of water and certain chemical elements in their magmas reduce the number of crystal nuclei that form. Water also allows pockets to form where minerals, like this beryl (variety: aquamarine), can grow unimpeded as large well-defined crystals.

Photo: E. Louis/© AMNH

#NewYorkRocks #crystals #gems #minerals #NaturalHistory #amnh (at American Museum of Natural History)
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