earthstory: digita1garden: Anybody know these rocks? The first…

earthstory:

digita1garden:

Anybody know these rocks?
The first is a green and black stone with large sparkly flakes in it.
The second is a pale purple with tiny sparkles and pink column-shaped crystals. It also has an orange/brown spot on the back that I didn’t get a pic of.

The elongate pink things look like tourmalines from the photo. Usually those are found associated with fluids coming off of a granite. I’m guessing based on the color these could be in a skarn deposit – maybe a limestone that got heated when a granite intruded next to it. The granite supplies the fluid and boron the tourmalines need to grow. My first test upon picking up this rock would be to try to use the white stuff to scratch something metal – if it can scratch metal then it is mostly quartz and this is probably a pegmatite, grown from the fluids coming off the granite. If you can scratch the rock with metal, then it probably is a skarn – made mostly of metamorphosed limestone.

The first looks as though it’s got some zoisite, which is a mineral in the epidote family. It commonly occurs with ruby, which is what I think the pink in that rock is. Was the rock particularly tough to cut through?

The second rock is mostly lepidolite (the purple sparkly stuff), and the pink is elbaite tourmaline. Both are Li-rich, which, along with crystal size, indicate that this is probably from a pegmatite deposit.

Geology Nerd