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Hodgkinsonite
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| Formula: |
Zn2Mn(SiO4)(OH)2 |
| Crystal
system: |
Monoclinic |
Space
group: |
P21/a |
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Occurence
Hodgkinsonite is an uncommon mineral known only from Franklin and
Sterling Hill, New Jersey.
It is a secondary mineral, and occurs as fracture fillings, in small
crystals, grains and masses. Most of the finer crystals, and more attractive specimens, came from the
Franklin mine.
Microscopic crystals present a remarkably complex form development. Most
of those visible to the unaided eye, however, are of very simple habit.
Hodgkinsonite is generally non-fluorescent, but some samples fluoresce
red under long-wave ultraviolet light.
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Much hodgkinsonite is a lovely lavender
color and quite transparent, though some is yellow, orange, or even nearly black due
to the presence of minute inclusions. In combination with
other unusual Franklin minerals the mineral provides collectors with beautiful mineral
specimens.
A classic occurrence includes opaque white plates of barite, and
transparent violet-colored masses and crude crystals of hodgkinsonite.
An example of this occurrence is shown in the photo on the left
(field width 4 cm). |
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Crystal structure
The crystal structure of hodgkinsonite includes
sheets of Mn-(O,OH) arranged parallel to {001}, which are bonded to layers of cross-linked
Zn-O and Si-O tetrahedra above and below, forming a second two-dimensional structure. Hodgkinsonite's
pronounced basal cleavage is likely due to this structural layering parallel to {001}.
Larger crystals of hodgkinsonite generally show the habit figured on the
right, and shown in the photomicrograph on the lower left of this page. Smaller
crystals (<0.1 mm ) often show a very complex development of forms modifying the
pyramid. |
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A large number of associations are recorded for hodgkinsonite. |
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Hodgkinsonite
crystal structure. Coordination polyhedra shown. Magenta: manganese; green =
zinc; cyan = silicon. Viewed looking down [100]; c-axis vertical.
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Hodgkinsonite.
Single crystal in vug, associated with a brassy, chlorite-like mineral. Franklin, NJ.
Width 1 mm.
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See
Dunn (1995) for discussion
and further information on hodgkinsonite.
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Hodgkinsonite.
Subhedral crystals filling a vein in willemite-franklinite ore. Franklin, NJ. Width 4 cm.
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