Unlike diamonds however (which are incredibly hard), opals are a relatively soft gemstone. Opals rank at about 5 or 6 on Mohs scale of mineral hardness, whereas diamonds rank at 10. To put this into perspective, opals are about the same hardness as glass.

Is Opal a hard or soft stone?

Opals are an extremely porous, soft and brittle stone so, there are a variety of reasons the stone can become discolored including but not limited to; exposure to water, cleaning solutions, soap, perfume and heat.

Is opal harder than glass?

GemHardnessBloodstone6.5 – 7Onyx6.5 – 7Moonstone6 – 6.5Opal5.5 – 6.5