Girls names that are stones?

This question is from my sister.
she is having twin girls and would like some name ideas. she would like to name them after stones like her other daughters.
she already has Krystle, Jade and Topaz.
so far she has come up with Ruby and Saphire
Their kitten is called amber lol so she wont use it! although it is very nice.
haha i suggested brick and cement block to her…she slapped me. so thanx for that dude.

Petra. It means stone.