Prehnite is a translucent to transparent gem-quality hydrated calcium aluminum silicate. It was the first mineral to be named after an individual, and it was also the first mineral to be described from South Africa, long before South Africa became one of the most important sources for precious and semi-precious gems.Prehnite is typically semi-transparent to translucent.Prehnite occurs in a range of green colors, including pale green to dark green and yellow- to brown-green. Prehnite may also occur gray, blue, orange, white and colorless. A soft apple green color is most desirable, while blue, pink, colorless, white and orange are considered the rarest occurrences and are highly sought after by mineral collectors.Prehnite is typically translucent in clarity and is rarely transparent. It is often found in very large sizes. Transparent and facetable material is typically found only in smaller sizes. Its has a vitreous to pearly luster.