This sample is spinel with calcite and is from Mogok, Burma. It is about 7x7 cm.
These spinel gems are 36.1 and 34.1 carats and are from Burma. "It is easy to confuse red spinels with rubies. They are found in similar places and have similar properties. The Black Prince Ruby in the British Crown Jewels is really a spinel! Impurities create many colors of spinel; red from chromium is the most prized."