Franklin Roberts' Photo Gallery
A5T-5R0Monazite-(Ce) Ce(PO4)
Dimensions: 6 cm x 4 cm x 4 cm
This 6 x 4 x 4 cm radioactive crystal assemblage of monazite-ce was found buried in the soil about 10 meters west of the Cactus Jack Pegmatite in 2008. Of the hundreds of monazite specimens collected since the pegmatite was discovered in 2005, about 80% have been recovered from the soil where they ended up after being eroded from the pegmatite. Sensitive gamma scintillation counters can easily detect buried monazite specimens such as this one at depths of up to a meter. This specimen is currently in the collection of Ed Gage, of Bandera, Texas.
12V-UEYFluorite CaF2
Dimensions: 10 cm x 7 cm x 7 cm
10cm x 7cm x 7cm nodule of massive emerald green fluorite from the Katemcy Batholith in Mason County, Texas. The specimen is back-lit to show its true color. This locality is a former topaz mine situated on a private ranch about 3 miles (5km) southeast of Katemcy, northeast of Mason. Ironically, this beautiful fluorite was considered as gangue by the miners and as such is found in abundance throughout the numerous tailings around the pit. Some of the fluorite masses uncovered are the size of soccer balls.
This green fluorite exhibits truly bizarre thermoluminescence. When strongly heated, it will begin to luminesce a bright white, which quickly shifts to canary yellow and then to a pleasing peach color. Over several minutes, the color will take on a reddish hue that will fade until the glow becomes dark magenta. Just before it appears to be fading to darkness, the familiar blue-green glow of chlorophane fluorite will again illuminate the specimen. This glow will then fade slowly until the fluorite is again dark. Unlike true chlorophane, when this fluorite has cooled, the beautiful green color will have been preserved without fading. Sunlight does not fade this material.
Mindat.org Photo of the Day - 7th May 2013
N8Y-LHPBeryl (Var: Aquamarine) Be3Al2Si6O18
Dimensions: 5 cm x 3 cm x 3 cm
5cm x 3cm x 3cm, 100 gram aquamarine fragment discovered in blast debris while opening a cavity in the milky quartz core of the pegmatite. This was one of two large aquamarine fragments uncovered by the shot. The other fragment may be viewed here: http://www.mindat.org/photo-329446.html
XWW-Y7GBeryl (Var: Aquamarine) Be3Al2Si6O18
Dimensions: 5 cm x 5 cm x 3 cm
5cm x 5cm x 3cm semi-hexagonal crystal fragment of beryl, var aquamarine, as found, in the debris of a small blast in the quartz dike at the center of the pegmatite. The blast was intended to open up a long central cavity that was discovered at a depth of 60cm while drilling the milky quartz. The cavity was later found to extend continuously for at least 20 meters through the center of the dike. A tiny color video camera and light source was lowered into a drill hole, revealing dozens of reflective crystal faces beyond the illumination zone of the small light source. A fair proportion of these reflections were green, possibly indicating the presence of gemmy aquamarine lining the walls of the cavity. A second piece of aquamarine, a fractured 100 gram blue-green specimen, was also discovered in the debris. It may be viewed here: http://www.mindat.org/photo-329447.html
Mine dump at former hoist shaft
This is one of several dump piles located around the capped hoist shaft of the White Eagle copper/silver mine. Many colorful copper minerals can be found throughout the spoil material with a minimum of effort. Metal detectors can uncover native copper and magnetite specimens from the piles as well.
7JV-9XUAzurite Cu3(CO3)2(OH)2 , Malachite Cu2(CO3)(OH)2 , Fluorite CaF2
Dimensions: 8 cm x 6 cm x 4 cm
8cm x 6cm x 4cm specimen of Azurite and malachite on tan fluorite, self-collected from the dump at the White Eagle copper/silver mine in Burnet County, Texas.
XHQ-9NYMolybdenite MoS2 , Microcline K(AlSi3O8)
This 4cm x 3cm foliated cluster of molybdenite was collected from a freshly shattered boulder of microcline that was winched from beneath 1 meter of water in the Petrick Granite quarry. The boulder was obviously rejected as dimension stone due to its "contamination" with molybdenite, fluorite and rare-earth minerals. It was dropped into the water sometime in the early 1940's and remained there until I discovered it during a dry period in 2007. By the time I had the equipment to haul it out of the pit in 2008, heavy rains had again inundated the boulder. As you can see, it was well worth the wait. The molybdenite has a mirror bright metallic luster with a pronounced blue cast. Several dozen equally impressive moly specimens were recovered from that rock.
Other minerals recovered from the boulder include gadolinite-Y, fergusonite-Y, yttrialite, powellite, uraninite and brownish-lavender fluorite, var. chlorophane.
Coal Creek Serpentine (Big Branch) Prospect
The Coal Creek Serpentine Prospect in Gillespie County, Texas as photographed looking northeast from the Willow City Loop. This occurrence represents the oldest rock unit in the state of Texas. Much of the serpentinite at this location is paramagnetic, probably due to inclusions of nickel and/or chromium. Native metallic inclusions can easily be seen with a 10X loupe.
This photo was taken in April of 2008. The bluish-green serpentine contrasts sharply with the pink precambrian granites and gneisses that surround it, even when seen from space. When viewed using Google Earth (30°28'46.12"N, 98°37'51.33"W), the color contrast is striking.
Yttrialite "asterism"
Dimensions: 1 cm x 3 cm x 6 cm
Cross section of a pegmatite boulder that was found to contain a pod of yttrialite in the form of an asterism (right of center). An asterism is a nodule of rare-earth mineral, in this case yttrialite, that is surrounded by a radial fracture pattern due to stresses induced by differences in the coefficients of thermal expansion between the pod and surrounding microcline matrix. As the pegmatite cooled, the microcline contracted around the incompressible yttrialite nucleus until enormous stress fractured the microcline. I am pointing to a 1x3x6 cm crystal of gadolinite sandwiched between two plates of biotite. The dark violet inclusions above the asterism are the "puce" variety of chlorophane fluorite initially discovered one mile to the north, at Baringer Hill, by William Hidden in 1905. This fluorite was found to glow softly in the dark at room temperature with no external excitation.
1UW-V1RK Feldspar (Var: Adularia) KAlSi3O8 , Microcline K(AlSi3O8) , Quartz (Var: Milky Quartz) SiO2 , Biotite K(Fe2+/Mg)2(Al/Fe3+/Mg/Ti)([Si/Al/Fe]2Si2O10)(OH/F)2 , Gadolinite
Freshly exposed 2 cm specimen of adularia exhibiting its characteristic blue schiller. A small group of 5-8 mm gadolinite crystals can be seen in the lower right.
