Qualitative XRD analysis led to identifying a variety of zeolite species, including analcime, as the dominant zeolytic phase, followed by chabazite, natrolite, thomsonite, wairakite, stilbite, stilbite-Ca, phillip-site and stellerite-Na, thomsonite-Ca, chabazite-Ca and chabazite-Na, with minor stellerite, laumontite
, levyne, phillipsite-Na, and gyrolite Other secondary minerals associated with zeolites were celadonite (Fe-rich mica), nontronite (Fe-rich smectite), greigeite (iron sulide mineral), koninckite or bobierrite (phosphates), alunite (sulphate), truscottite (silicate), calcite or dolomite, and quartz Nontronite occurred in most samples.
Shortly thereafter, the group found a large zone rich in minerals including laumontite
, stilbite, quartz, heulandite and (the most spectacular of them all) calcite.
is milky white and subvitreous to vitreous.
From the Komsomol mine: clusters of green ktenasite microcrystals; acicular tufts of white thaumasite; tabular apophyllite crystals to 5 cm, some of them water-clear or showing growth zones; transparent, rhombohedral crystals of calcite in clusters to 5 cm; white okenite "puff balls" to 6 mm; attractive clusters of orange stilbite crystals to 6 cm; clusters of attractive pink laumontite
to 6 mm; and sharp, lustrous pyrite crystals on pink apophyllite-encrusted matrix to 8 cm across.
Some of the fluorite crystals are of a "standard" pale pink but the color-palette also includes colorless, pale yellow, pale green, medium-green, color-zoned pink/green, and rose-red; the most common associated species are quartz, adularian orthoclase, titanite and laumontite
(Gramaccioli, 1975; Preite et al., 1997).
A number of other zeolites have also been reported from Merelani, including laumontite
and mesolite in tufts of acicular white crystals, and stilbite, scolecite and chabazite-(Ca).
At locality 44, pseudomorphs of albite after trapezohedral analcime crystals up to 1 cm were found in fine-grained, massive laumontite
associated with meionite, titanite, fluorapatite and rare zircon.
Pandey showed me several lustrous, terminated prisms of gypsum to 30 cm long, some with areas in which small included laumontite
crystals may be seen through the water-clear body of the host crystal.
The locality is said to be a basalt flow, and there are also microcrystals of laumontite
and apophyllite on a few specimens.
Over the years, Tom and I have encountered just one zeolite, laumontite
, on Green Monster Mountain.
Associated minerals are: elbaite, lepidolite, danburite, boron-rich muscovite, laumontite
, quartz and albite.