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Hardness measures 7.0 to 7.5 on the Mohs scale – the Mohs scale measures the hardness of metals, minerals, gemstones and crystals on a scale of 1 to 10. For example the hardness properties of most quartz crystals fall around 7 on the scale, as does steel and titanium. Diamond is the hardest known substance on the Mohs scale coming in at a hard 10. To most consumers hardness generally reflects the stones able to resist scratches and cracks.
The cleavage in tourmaline is poor.
The index of refraction ranges between 1.610 and1.735 and generally indicates the purity of the stone.
The specific gravity is ranges between 2.96 and 3.31.
The crystalline system is hexagonal rhombohedral.
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