<ul><li>Optical Calcite - Bulk Mineral</li></ul><br><br>Calcite is the most common mineral next to quartz. Optical calcite is less common. It is shaped sort of like a rectangle which has been stretched (a rhombohedron). It is clear with a glassy luster and makes objects placed behind it appear double (due to different indices of refraction of light it has). Flawless specimens are used in optical instruments. Great for science projects or classroom collection. Please be aware that this is a natural mineral and as such each piece is one of a kind! The one you receive may not be exactly the same as the ones pictured but it will be similar. Price is per each piece.They come in irregular shapes, sizes and weights. Photo shows three pieces for demonstration purposes only. Recommended for ages 7 and older.