From where do the gems used in jewelry come

Caves. Diamond miners mine them. Most gemstones form in the Earth's crust, approximately 3 to 25 miles beneath the Earth's surface. Two gemstones, diamonds and peridot, are found much deeper in the Earth. Diamond forms in "kimberlite pipes" that originate in the Earth's mantle and end at the surface.

Gems are mined from places around the world. they have a diamond mine in Canada and have some in Brazil. The colors of gems are caused by different things if its blue its from the cause of boron for an example