FLUORESCENT MINERALS AT THE OMYA WHITE KNOB QUARRY, LUCERNE VALLEY CALIFORNIA

Omya, the leading global producer of ground calcium carbonate, produces white calcium carbonate from the White Knob quarry located on the north slope of the San Bernardino Mountains in the Lucerne Valley area of the Mojave Desert California. The quarry is developed in multiply folded, Paleozoic miogeoclinal carbonate rocks intruded by a variety of Mesozoic age plutonic rocks. The Monte Cristo Limestone of Mississippian age has been multiply metamorphosed to amphibolite grade, forming very coarse grained white calcite marble. Mining is by standard open pit methods. Ore is processed into fine grind calcium carbonate and utilized in hundreds of common consumer products.

Fluorescent minerals are common in waste rock and not in the high purity calcium carbonate ore. Fluorescent minerals respond to short wave ultra violet light. White Knob is the most prominent fluorescent mineral location in Southern California.

Fluorescent minerals have several modes of occurrence at the quarry. Most occur within the Arrowhead Member of the Mississippian Monte Cristo Limestone, originally an impure cherty limestone, metamorphosed to wollastonite calc-silicate marble. Several Mn bearing minerals are present. Fluorescent minerals are also common in the Arrowhead including orange fluorescing calcite, bright yellow wollastonite, lime green hyalite and aragonite, blue diopside, white dolomite and unknown minerals that fluoresce violet, azure blue, sky blue and shades of olive green. Another common fluorescent mineral occurrence is magenta fluorescing feldspar, within Jurassic granite dikes. When the dikes cut the fluorescent Arrowhead Member, spectacular multi color specimens are present. Other common fluorescent occurrences include highly phosphorescent travertine and caliche. Less common are skarn occurrences including metallic minerals such as powelite (a molybdenum mineral) which fluoresces as bright white snowflakes.

The presence of activator impurities in the host rock including Mn, U, Zn, Fe and REE are likely responsible for the fluorescence at the White Knob quarry. Fluorescent minerals occur in rocks of different ages and include primary minerals, metamorphic minerals, and secondary minerals. Genesis is related to inherent composition as well as other processes occurring over a range of geologic time.