Azurite

Azurite is probably the rarest thing you can ever find if you find it at the Basalt, and it still is super rare in the Abyss. Azurite is worth 5000 Gold Coins per piece. Azurite looks like Quartz at far range but if you look at Azurite closer, it is Blue, and azurite also has the same Material as Quartz does. Azurite mining speed can be increased by going to Delrim (The Blacksmith) and buying a Ore mining speed upgrade.

Here is a picture of Azurite