Sapphire, birthstone for September
The origin the of birthstone is believed to have originated in the book of Exodus in the Bible.
Aaron had 12 gemstones set into his breastplate ( a protective ancient 'stab jacket' ) with each different jewel representing each of the lunar months.
There are many substitutes available for the most precious gemstones.
September's birthstone happens to be Sapphire, which is classed as a precious stone. However, in Victorian times the semi precious Iolite gemstone was referred to as a 'Water Sapphire', though it has no physical connection to the real one, and was used as a substitute.