Selenite (mineral) was filled with mineral-rich water that drove the crystals' growth. The largest of those crystals weighs 55 tons, is long, and is over 500,000 years old. Gypsum occurs on every continent and is the most common of all the sulfate minerals. Gypsum is formed as an evaporative mineral, frequently found in alkaline lake muds, clay beds, evaporated seas, salt flats, salt springs, and caves. It is frequently found in conjunction with other minerals such as, copper ores, sulfur and sulfides, silver, iron ores, coal, calcite, dolomite, limestone, and opal. Gypsum has been dated to almost every geologic age since the
Vegetation of open habitats in the British National Vegetation Classification system up this category: Vegetation of open habitats in the British National Vegetation Classification system This article gives an overview of the plant communities formed by vegetation of open habitats in the British National Vegetation Classification system. The open habitat communities of the NVC were described in Volume 5 of "British Plant Communities", first published in 2000, along with the three groups of maritime communities (shingle, strandline and sand-dune communities, salt-marsh communities and maritime cliff communities). In total, 42 open habitat communities have been identified. The open habitat communities consist of eight separate subgroups: The following is a list of the