Transparency, also known technically as diaphaneity, is a function of the way light interacts with the surface of a substance. There are only three possible interactions. If the light enters and exits the surface of the substance in relatively undisturbed fashion, then the substance is referred to as transparent. If the light can enter and exit the surface of the substance, but in a disturbed and distorted fashion, then the substance is referred to as translucent. If the light can not even penetrate the surface of the substance, then the substance is referred to as opaque. Many substances that are transparent can easily contain flaws and distortions that will limit a light beam's travels through a substance and make it translucent.

Some Transparent Examples:


Transparency, simply by a lack of differing possibilities, is not a very important property. However, It can come into play if all other properties are inconclusive and/or can provide some assurance of an identification if needed. Certainly if an unknown mineral is translucent, a collector would feel rather foolish to have identified it as a mineral that is always opaque!

It is rare for an opaque mineral to have any translucent specimens, however, some translucent mineral specimens can become opaque from inclusions or weathering effects. Sphalerite is one example of a normally opaque mineral that often surprises collectors with an occasionally transparent specimen. Although a transparent mineral will always have some samples that are translucent (due to flaws, etc) it may be helpful to know if a mineral is typically transparent or vise-versa. And occasionally, a mineral that is translucent may never be transparent and knowing this can be very helpful to a collector. In listing a mineral's transparency these factors are taken into account to aid the collector as much as possible.

Another consideration is that a transparent mineral may be so strongly colored as to appear opaque. Azurite is an excellent example of this, as the extremely deep transparent blue crystals may appear black and opaque. However, near-surface internal fractures, and sometimes crystal edges when viewed against a bright light, can reveal the true color and transparency.


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