Like the tourmaline, its companion birthstone for October, the opal is noted not only for its unique beauty, but also for its wide range of variations. Opals range from precious--displaying an iridescent play of color under changing light--to the common, which may be multi-toned but do not appear to change between viewing angles.
At a 6 - 6.5 on the Mohs scale, the opal is one of the softer gemstones and should be kept from contact with hard or rough surfaces. Like the pearl, the opal requires a certain amount of moisture and should not be kept in excessively dry environments such as airtight safes. And also like pearls, opals should not be ultrasonically cleaned due to their relative softness. As with most gemstones, soap and warm water with a soft cloth is a safe method of cleaning.