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Rubies have a compactness of 9.0 on the Mohs dish of mineral compactness. Among the natural gems only crystallized carbon is harder, with a Mohs 10.0 by exact meaning.

All natural rubies have imperfections in them, including tint impurities and inclusions of rutile needles known as "silk". Gemologists use these needle inclusions found in of nature rubies to mark out them from synthetics, simulants, or substitutes. Usually the uneven stone is heated before sharp. Almost all rubies today are treated in some figure, with heat usage being the most common frequent repetition. However, rubies that are completely untreated but still of of the highest order quality require a large prize.

Some rubies show a 3-sharp end or 6-point asterism or heavenly body. These rubies are cut into cabochons to unfold the effect suitably. Asterisms are most excellent visible with a one only-light rise, and move across the stone as the medium of vision moves or the bowlder is rotated. Such furniture occur when medium of vision is reflected off the silk (the structurally oriented rutile needle. inclusions) in a indubitable way. This is one example where inclusions enlarge the value of a gemstone. Rubies can moreover show color changes — though this occurs very seldom — and chatoyancy.

Source: Precious Gemstones from Japan