1) Brightness 2) Iridescence 3) Milky luster 1) Iridescence 2) Semitransparency 
Opalescence is a type of dichroism seen in highly dispersed systems with little opacity. The material appears yellowish-red in transmitted light and blue in the scattered light perpendicular to the transmitted light. The phenomenon is named after the appearance of opals. There are different degrees of opalescent behaviour. One can still see throug...
a reflection of a milky or pearly light from a gem's interior, sometimes used as a synonym for irridescence.
milky iridescence
• (n.) A reflection of a milky or pearly light from the interior of a mineral, as in the moonstone; the state or quality of being opalescent.
Opalescence is a type of dichroism where a gem appears yellowish-red in transmitted light and blue in the scattered light perpendicular to the transmitted light. The phenomenon is named after the appearance of opals . This effect can be seen in nature in the way the sky is blue in the daytime and yellowish-red at sunset.
Milky or pearly appearance. Girasol.
Effect seen in a few minerals, chiefly opal (hence its name) which cause it to exhibit a glimmer of different colors when rotated or seen in different angles. Opalescent describes mineral exhibiting this effect.
O`pal·es'cence noun (Min.) A reflection of a milky or pearly light from the interior of a mineral, as in the moonstone; the state or quality of being opalescent. 
[n] - the visual property of something having a milky brightness
pearly or milk-like reflections that appear to come from within any material so 
Milky blue or pearly appearance of the common opal.
iridescence noun the visual property of something having a milky brightness and a play of colors from the surface