finely dispersed fluorite gives this Fluorite-Opal-Jasper (»Tiffany Stone«) it's purple color
Foto: K. Sieber, www.makrogalerie.de
At the beginning of the millenium many tumbled stones we sold under the trade names »Tiffany Stone« and "Fluorite Opal".
This beige rock with violet veins, which is known in the USA as "Tiffany Stone" is provided by a large number of small deposits in southwestern Utha (USA), which came to be known as "Spore Mountain Lavender Mines". In Europe tumbled stones were sold under the name "Fluorite Opal".
The rock owes its formation to the activity of volcanoes, which deposited in several eruptions large quantities of silica-rich ash layers in an area dominated by limestones. Between the sporadic eruptions quartz-rich sediments were gradually solidified and transformed. Fluorine-containing gases led to an impregnation of the sediments with fluorite. In an older period mainly quartz, quartzite, jasper, agate and flint were formed along the contact to the underlying limestone. Manganese ores associated with the limestone, were incorporated and form brown to black, often metallically shiny veins in the rock.
In a later period opal-rich concretions (opalite) were formed, either in the still soft volcanic ash or between the old limestone horizon and the soft ash. This eventful history finally led to the interestingly patterned rock, which is composed of different quartz modifications (opalite, jasper, agate, flint), fluorite and manganese ores.
From a mineralogical point of view, rocks that are called "Fluorite-Opal" should be an opaline rock ("Opalite"), impregnated with fluorite. However, due to the brittleness of opal and fluorite, this material couldn't be processed as a tumbled stone. When we examined some tumbled samples of the socalled "Fluorite Opal", we found a mix of Jasper and finely crystallized quartz impregnated with fluorite. The high concentration of Jasper makes the material less brittle and harder than Opalith. In this composition it is suitable for the manufacturing of tumbled stones. For these stones the name "Fluorite Opal" is misleading, as the main part of this rock is jasper and not fluorite nor opal.
Fluorite-opal-jasper, as shown in the picture above, consists of purple areas of fluorite and brown areas of manganese oxides finely dispersed in beige jasper. Opal occurs in fissures or as an impregnation in very small amounts only.
Opaque, beige, tumbled stones with few or no purple parts consist solely of Jasper. Therefore they should be called "Jasper" and not "Fluorite Opal".