This specimen consists jet black
pyrochroite with bladed crystals of colourless
barite
and scattered light reddish brown coloured crystals of allactite. There are
also small spherical masses of
brandtite
found scattered primarily on the
pyrochroite. The largest allactite crystal is a flat lying 2.5 mm across
and it is also a doubly terminated crystal. The
pyrochroite in this specimen was actually a rare form called backstromite.
This form is equally susceptible to rapid alteration. Though the original form
is still present the mineral has in fact altered to
hausmannite and
feitknechtite - both oxides of manganese. Backstromite is an obsolete term
for
pyrochroite.
This specimen consists almost entirely of
calcite.
There are two exposed veins, however, which are lined with brownish coloured
crystals of allactite and colourless
barite.
The crystals of allactite are small but abundant where they are found on this
specimen. The largest crystal is perhaps 1mm across at best.
This specimen consists jet black
pyrochroite and deep reddish brown coloured, moderately translucent
allactite crystals. Also present are crystals of
lead and
pyrochroite. The lead occurs as cubo-octahedral crystals with varying
degrees of surface alteration to
hydrocerussite and jet black splotches of (manganese or lead oxide?). The
allactite has suffered along with the deterioration of the
lead
through the oxidation process since as it oxidized it expanded weakening the
allactite crystals.
Origin: Långban, Sweden
Harry von Eckermann Collection
Sample size: 9.5 x 6.5 x 5.5 cm (top/2nd/3rd row), 11.3 x 6.5 x 4.5 cm
(4th/5th row), 6.2 x 5 x 3 cm (6th/7th/bottom row)
