Other secondary minerals are carbonate, sericite, prehnite
, titanite, chlorite, and minor epidote and hematite.
La chlorite, la prehnite
et la pumpellyite mineralisee de facon eparse presentes, indiquent que les roches ont atteint le stade d'un facies a prehnite
The sheet dykes are often crushed along different directions and are filled with Prehnite
The left label shown here is from the Mineralogical Record Label Archive (from Ron Bentley's collection), and the one on the right (still attached to a prehnite
specimen) was recently shown to us by Kelly Nash.
Although not a major producer of collector-quality specimens, it has yielded fine examples of heulandite, stilbite, calcite, chalcedony, datolite and prehnite
fine-grained aggregate of epidote group minerals, albite, prehnite
, sericite, and possibly clays).
The regular octahedrons rest on colorless and smoky quartz and are accompanied by other minerals including prehnite
, sphene and adularia.
Beautiful yellow-green, transparent prehnite
in spheres, hemispheres and "crests" on matrix of graphite-infused rock, from the Merelani mines, Arusha, Tanzania--see the photos in the recent "Tanzanite Issue" (September-October 2009)--has sold for rather high prices in some quarters during the past three years or so, but excellent toenails and small miniatures of the material could be had for $15 to $45 from The Crystal Circle, LLC (www.
, calcite and sulfides were the main constituents found within the irregularly shaped vugs of this structure.
Around 2000 John Saul saw quite a few prehnite
specimens from Merelani, but they were all badly battered.
The specimens came from a collecting site in the mine (now completely exhausted) discovered at some time between 1996 and 1999 by a young geologist from Thetford Mines, who originally classified the mineral as prehnite
The mine at Asbestos produced wonderful specimens of orange grossular ("hessonite") garnets and some of the best prehnite
, pectolite and vesuvianite specimens in the world.