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The MOHS Hardness Scale

1Talc/GraphiteCan be scratched with fingernail
2GypsumCan be scratched with fingernail
3CalciteCan be scratched with Copper
4Fluorite/MalachiteCan be scratched with knife
5ApatiteCan be scratched with knife
6Feldspar/AmazoniteKnife barely scratches it
7Quartz/AgateScratches glass easily
8TopazScratches Glass and common minerals
9Ruby/SaphireScratches Topaz and common minerals
10DiamondScratches Topaz and common minerals

Helpful Hardness Tips

It is generally beneficial to tumble rocks of the same kind or of the same hardness together. Jaspers, Agates and Quartzes all have a hardness of approximately 7 to 7 1/2 and thus can be tumbled together. Rocks in this hardness range will be easiest for beginners. Amazonite, Labradorite and Unakite are all in the Feldspar family at a hardness of approximately 5 1/2 to 6 and can be tumbled together. It is recommended that when tumbling stones of this hardness that an extra step of 1000 Grit Aluminum Oxide be run before the polish stage for 2 to 3 days. Apatite, Fluorite, Malachite, Turquoise, Petosky stones and others are at hardness’s of 4 to 5 and in some cases will need special techniques to polish such as polishing dry in Corn Cob. Stones with hardness’s of under 4 may not polish at all or will only take a light shine. It should be noted that some stones have certain textures, grains or combinations of hardness’s which will make it challenging to get a high polish. Jade is a good example of this. Rocks with hardness’s of 9 or above are very difficult to tumble. Rubies and Saphires fall into this category and are not a good choice for beginners as they will likely frustrate you and turn you off of tumbling all together.

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