Green

Agate

Limb

Cast


 
It is always exceedingly exciting to find green stones in the high desert. The local is usually steeped in great amounts of brown dirt and beige dust. If one carries a water bottle, you can see right away that you have something in great contrast to the rest of the gravel and dirt clods. If one carries a light, you can see the material is clear or translucent with very interesting green inclusions.
 


 
First off, a 'limb cast' is a casted mineral impression of a tree limb that became encased in rock. In many of the cases in the high desert of Oregon, the limb casts are formed when the ash from a volcanic event settles around a limb (sometimes incinerating it) creating a pocket that has the exact shape and texture of the limb. Often the ash material is high in silicates and those leach into the pocket by way of water. If, in addition to silicates, there is a mineral present in the 'silicate soup', colors may form in the hardening new rock formation within the cast. If the minerals present oxidize green, you get green limb cast. Under the right conditions, dendrites grow and you have 'moss agate' limb cast.
 

 
These pieces of 'moss agate' are from limb casts we found in the Paulina, OR. area. The outside of the rock that bore these was a perfect impression of the wood branch complete with striations. Inside, there were both pockets of the light green dendrites, but also pockets of fortification agate with a blue tint and druzy quartz chambers. Material like this makes getting inside the rock and polishing it nothing short of exhilarating.  
Daily Visions April-14-2017
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Featured Artist April-14-2017
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