Turritella Agate Johanna E

Turritella Agate Johanna E. Forsh [email protected]

What is an agate? temperature changes and the “fill- ing in” process, each agate will look An agate is a crystallized rock, different and have different colors which forms from Chalcedony, a and banding patterns. kind of silica, or quartz minerals. Ag- ates are characterized by their grain textures and commonly have bright Turritella or Elimia tenera? colors. Many agates can be found in The “Turritella” agate is not volcanic rocks but are also common actually fossilized snails of the ge- in metamorphic rocks. An agate is nus Turritella, but is of the Elimia formed when water, rich in quartz tenera species, formerly known as molecules and other minerals, fills Goniobasis tenera. E. tenera was so into small hollow spaces in rocks. named “Turritella” ag- The quartz molecules later form ate because of its microcrystals that attach to resemblance to the the sides of the hol- genus of sea snail low spaces. This Turritella which process repeats has been com- multiple times monly found until the rock is in Texas and completely filled California. The in. Because the Elimia tenera process is re- however, are peated, band- freshwater ing patterns snails com- are often mon to the visible. De- now Wyo- pending on the variety of minerals,

All images © Johanna E. Forish ming area and are shorter and wider The fossils are generally found than actual Turritella snails. These in the areas of southern Wyoming, snails are now extinct but lived dur- northern Colorado and northeastern ing the Eocene Epoch, which lasted Utah. E. tenera can be found in the from approximately 34-55 million sedimentary rock layers of the Green years ago. The fossil beds that the River Formation, a tributary of the Elimia tenera were found in are ap- Colorado River. The Elimia tenera proximately 46-51 million years old. was washed up near the shorelines of a series of small lakes, give the names: Fossil, Uinta and Gosiute Characteristics Lakes. The best samples come from the Gosiute Lake area. These areas E. tenera snails are character- once had a subtropical climate and ized by their long spiral shells which were prone to volcanic eruptions. Be- contain many whorls. Their color cause of this climate, the fossils were can vary from amber, gold, blue, or able to be agatized. red and orange in a gray or black to dark brown milieu. The snails were of medium size and could Scientific Classification grow up to 1 ½ inches Kingdom: Animalia long. Phylum: Mollusca Class: Gastropoda clade: Caenogastropoda clade: Sorbeoconcha Superfamily: Cerithioidea Family: Pleuroceridae Genus: Elimia Species: Elimi tenera Synonyms: Goniobasis tenera Equipment Magnification and Stacking The equipment I used for these images were: I photographed the Elimia tenera ag- Camera: Canon Rebel XSi ates from 1-5x magnification. File format: Raw Each image shown in this article has ISO: 100, 400 been stacked using Zerene Stacker Fstop: F16 software. Each image has between 3 Shutter speeds: ¼ second - 8 seconds and 16 images compiled together to Lenses: Canon MP-E65mm f/2.8 1-5x obtain the optimal focus throughout Macro Photo, Canon EF28-135mm the entire image. I compiled the im- f/3.5-5.6 IS USM. ages using the PMax stacking method rather than the DMax method. I I also used a copy stand to mount found that PMax gave a better over- the camera, fiber optic lights and a all sharpness to the images. variable height stage. The fiber optic lights were placed on either side of the subject with plastic balls on the ends for diffuse lighting. All images © Johanna E. Forish Sources:

http://www.priweb.org/Research/Turritella%20 If you have any questions, comments Agate.htm or concerns please feel free to contact me at [email protected] http://www.stoneageindustries.com/turritella_ agate_goniobasis.html

http://www.agatelady.com/agate-basics. html#how_do_agates_form

http://en.wikipedia.org/wiki/Agate

http://en.wikipedia.org/wiki/Elimia_tenera