These are Thomsonite crystals a rare
zeolite mineral created in a small area of lava flows along Lake Superior in Minnesota, U.S.A.. The stones grew in gas-bubbles
(amygdules) and in seams left when the lavas cooled and became solid rock, around 600 million years ago. The crystals
grew slowly as radiating needles when mineral rich ground water permeated the ancient basalt lava.
The stones polish well and can
display amazing chatoyant "eyes" ! They have a hardness of 5 to 6, dark areas in the stones can be softer.
These nodules have been tumbled in fine grit just long enough to expose colors then tumble polished. Some have
become well rounded and smooth and have a nice shine. Others are oddly shaped and partial crystals some are tiny but nearly perfect.
I have had good luck re-shaping them into cabochons with 1,400 mesh diamond belts or well worn 600 grit sanding
wheels. To get a high polish 14,000 mesh diamond paste or cerium oxide works well.
Each parcel weighs 1 ounce (about 28 grams).
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