Geopic of the week: Arkansas Wavellite

The above picture shows two examples of the mineral wavellite: an aluminum phosphate mineral prized by rock and mineral collectors and fairly common in the Ouachita Mountains.  The green sample on the right is the typical color of wavellite, whereas the blue sample is a rare form.  The green color is due to the presence of vanadium.  These samples were both collected from an abandoned quarry a couple of miles northwest of Mt. Ida, Arkansas.

It’s easy to see why mineral collectors would be interested in wavellite as it comes in a variety of attractive colors – rarely white, yellow and black in addition to the blue and green examples shown here. It also has a visually interesting growth habit; it grows in botryoidal (grape-like) spheres that internally consist of a radiating array of slender crystals that resembles an eye.  Examples of this eye-like structure can be seen by clicking on the “more views” link below.

Wavellite is also quite sparkly and Christmassy.  I even hear it’s the official mineral of the north pole.  Ho ho ho!

To see more views of Arkansas wavellite click here

Geopic of the week: Dinosaur tracks in Arkansas

Pictured above are tracks of an Acrocanthosauras Atokensis: a bi-pedal predatory dinosaur.  The tracks were discovered in 2011 in a gypsum mine north of Nashville Arkansas by workers at the mine.  It is one of two such “dinosaur trackways” – as they are called – that have been discovered in this mine;  The first one was unearthed in 1983.  Dinosaur tracks are not common in Arkansas as most of the rocks here, which are very old, were deposited long before the dinosaurs existed. 

The rocks where the tracks are preserved were deposited in the early Cretaceous Period sometime between 145 and 100 million years ago.  At that time, the area south of the Ouachita Mountains was a broad coastal plain and the Gulf of Mexico waters reached all the way to southern Arkansas.  A variety of dinosaur species tracks, both herbivore and carnivore, have been discovered in these trackways, indicating that the coastal area at that time was quite the dinosaur stomping ground.