Geo-pic of the week: Pegmatite from Magnet Cove

Agerine from Magnet Cove, AR

In the picture above, large black rectangular aegerine crystals are prominent in a rock type known as a pegmatite.  Pegmatites are igneous rocks characterized by extremely large crystals.  Sometimes they also contain unusual mineral species.   This sample was collected from Magnet Cove, Arkansas.  Magnet Cove, which is approximately 10 miles east of Hot Springs, is one of the few places in Arkansas where igneous rock is exposed at the surface. 

Between 84 and 100 million years ago, magma was injected into the earth’s crust under central Arkansas where it slowly cooled and crystallized into igneous rock.  Millions of years of erosion eventually unearthed that rock.  Despite only being exposed over approximately 5 square miles, the rocks of Magnet Cove have yielded more than 100 different minerals.  Rare minerals have been discovered there including a new variety of zirconium-rich garnet called Kimzeyite.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s