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
Interlanguage fossilization opinion. The term, borrowed from the field of paleontology, conjures up an image of dinosaurs being enclosed in residue and becoming a set of hardened remains encased in sediment. The metaphor, as used in SLA literature, is appropriate because it refers to earlier language forms that become encased in a learner's interlanguage and that, theoretically, cannot be changed by special attention or practice of the target language. Despite debate over the degree of permanence, fossilization is generally accepted as a fact of life in the process of SLA. Many researchers have attempted to explain this. Workers have attempted to discover: