Barite mineralization associated with botryoidal speleothem crusts was sampled in the southern and western parts of the quarry (Fig.
In the cave structures filled with botryoidal calcite speleothems the barite and pyrite successions are covered in curved-face columnar-bladed calcite aggregates that grade into a finely laminated calcite aggregate (Fig.
The [delta][.sup.18]O values of calcite crusts, increasing from -11[per thousand] in the central parts of the botryoidal aggregates to -5[per thousand] in the outer parts of the aggregates suggest the cooling of the low-temperature hydrothermal fluid from ca 70 [degrees]C to ambient temperature (Eensaar et al.
Three polished pieces were prepared by Jacques Le Quere (JackyGems, Auray, France) for this research: one round brilliant (1.32 ct), one flat rectangular cabochon (1.81 ct) and one piece with the botryoidal surface kept on one side and a rounded cabochon polished on the other side (0.83 ct).
The rough specimens showed a botryoidal or concretion-like morphology (e.g.
Chrysocolla pseudomorphs of botryoidal malachite (to 4 mm) with hemimorphite have also been found in float.
Green botryoidal duftite-conichalcite (2-3 mm) has also been found associated with mimetite at one location in the Brown Monster mine.
It is also found in lavender botryoidal
specimens up to 2.5 cm thick.
Specimens from this occurrence remain the finest known examples of botryoidal mimetite in the world.
On the 9th level he found a vein of mimetite which he dug into, and which opened up into a large cavern measuring 20 X 30 X 40 feet, entirely lined with beautiful botryoidal yellow mimetite.
It was lined with bright orange botryoidal
pyromorphite aggregates grading into green crystals of classic hexagonal, hoppered shape.
But the main reason Magdalena is on the map of world-class mineral localities is the occurrence there of beautiful blue-green (so-called "Kelly blue") smithsonite in large botryoidal
growths, sometimes with "rice grain" crystals of blue-green smithsonite on top.