Opal-(CT) var: Lussasite

Item Description

A rarely seen specimen of Opal-CT, a variety of Opal which is said to get its name from Cristobalite and Tridymite content, but according to the entry on the mindat.org, "Fröhlich (2020) found no evidence for the presence of cristobalite in some samples of this material, and Fröhlich found the material to be a mixture of non-crystalline (X-ray amorphous) material and poorly crystalline blades of low temperature tridymite". This specific specimen is from the Les Rois Mine in France, and is a further variety referred to as "Lussasite". The piece features a coverage of gemmy, golden spherical groups with individual balls measuring up to 4 mm across on matrix. Typically the Opal-CT from this locality is a soft blue color, but some of them have inclusions of Petroleum var: Bitumen, and that's probably the case with this piece. A cool rare locality specimen for anybody who likes Opal. The piece shows an intersting fluorescence with areas of bright white that show up under LW UV light and other portions of the "balls" show a muted golden-brown hue.
From the collection of Colin Manlove.