In the early 70’s a small deposit of bright yellow fluorescing quartz was discovered near the town of La Sassa, Tuscany, Italy. The unique mineralogy (fluorescent quartz in crystalline form) was a notable find. Pieces were analyzed at the time and it was decided that the fluorescence was not due to hydrocarbon inclusions as seen in some Herkimer type quartz crystals today. The nicest pieces from this find were mined and sold - no new material has appeared until today. (There have been offerings of massive yellow fluorescing quartz from this area, but the fluorescence is rather dull compared to this material, and the habit is massive/rough crystals). Equally fluorescent all wavelengths.
These pieces from a small discovery by the nephew of the fellow who made the original find. They are described in literature as being “geyser eggs” - semi-translucent white concentric bands of radiating quartz. The quartz is fluorescent a very bright yellow - can easily compete with the brightest apatite from Pakistan, or even powellite from India. Only a few pieces are available as this came from a find in his basement (not in the field). The nodules are embedded in a calcite matrix, slightly fluorescent (etched to reveal the crystals).
A study released by Guido Mazzoleni in 2013 details the suspected activators of the La Sassa quartz: “it is probable that the fluorescence of La Sassa quartz is due to the presence of (UO2)2+, Tb3+, Eu3+, Dy3+, and quantitatively subordinate Ce3+, and Sm3+ centers. Even at a few ppb, Ce3+ affects the fluorescence, since it transfers its excitation energy to Tb3+, intensifying the green emission (maximum around 544 nm). Eu3+ and Dy3+ shift the fluorescence response toward the yelloworange region of the spectrum, while the uneven presence of (UO2)2+ shifts the response towards the green region.” (from LUMINESCENCE SPECTROSCOPY: A POWERFUL TOOL FOR STUDYING HYDROTHERMAL MINERALS. THE EXAMPLE OF REE-DOPED SILICA PHASES IN ASINTER DEPOSIT CLOSE TO LARDERELLO GEOTHERMAL FIELD, ITALY- Jun 2013)