You can buy a birefringent (https://en.m.wikipedia.org/wiki/Birefringence https://en.m.wikipedia.org/wiki/Birefringence) calcite crystal that are often sold at

You can buy a birefringent (https://en.m.wikipedia.org/wiki/Birefringence https://en.m.wikipedia.org/wiki/Birefringence) calcite crystal that are often sold at rock shops and give it a try.