Native American Post Earrings

The green / blue stone in these earrings will look great with jeans, or a casual skirt. They have a southwest feel to them. These were purchased at a Native American fair in Arlington, TX in 2005. I can’t read the stamp on the back, but it looks like It starts with “A MA”, and appears there may be another stamp over the name. I can’t remember what the stone is called. I don’t know if these are silver, but I know I’ve had to polish them up before wearing.