Open Adit™ - Mineral Properties / Diaphaneity

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Diaphaneity refers to the degree to which a material transmits light. Traditionally, three terms have been used in describing the diaphaneity of minerals: transparent, translucent, and opaque. Transparent means that objects can be seen clearly through a crystal; translucent means that a crystal will transmit light, but an object cannot be discerned through it; and opaque is reserved for minerals that do not transmit any light.

Because no set standards apply, the size of a crystal greatly influences its diaphaneity designation. A large number of rare species found only in crystals of microscopic size have been described as transparent. It is possible that if these species had been found in cabinet size crystals, they would have been described as translucent, rather than transparent.

Many minerals that are considered cabinet size specimens would usually be considered translucent, but in very thin plates they can actually be transparent. Often a rather large crystal will appear opaque, but in small pieces or thin plates it is translucent. One particular metallic mineral, molybdenite, like virtually all other sulfides, is always described as opaque; yet because it has an excellent basal cleavage, similar to that of a mica, it can be separated into cleavage plates that are so thin they transmit some light. So, in many or most cases, the degree of diaphaneity of a mineral really comes down to crystal size and / or shape.

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