Sidcup Lapidary & Mineral Society

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Minerals, Crystals and Gemstones
containing
Inclusions
evening


M
onday 1st February 2011
Almost a full house of members turned out for this evening as well as a few prospective new members.
I think an enjoyable evening was had by all.

Inclusions are for the most part microscopic minerals, (solid,liquid or gas) found within a host mineral, crystal or gemstone - trapped as part of the growth development of the host crystal.
Inclusions formed before the development of the host crystal are termed PROTOGENETIC (Solid inclusions only). Those formed and trapped simultaneously with the host are SYNGENETIC (solid, liquid or gas). EPIGENETIC inclusions are those developed after the growth of the host crystal.

On the evening a number of small displays from personal collections were on show. One or two facetted gemstones were on view but one Fluorite Egg from France (Margaret’s collection) had a curious colourless crystal trapped within. A number of suggestions as to its identification were made but no final conclusions could be drawn.


A selection of near transparent quartz crystals from Ireland was on display from Paul’s collection. All self collected, these had microscopic inclusions of dark gray-green chlorite suggesting that these might be from an alpine type deposit. Another superb quartz crystal group from Switzerland showed a similar association.

A computer slide show of inclusion images was on show and a few members brought microscopes to help view some of the inclusions in crystals brought in by other members.
Here are one or two of the items that created interest:


An array of parallel grown negative crystals within a fragment of quartz from Wales.


Hematite "Ribbons" trapped inside a facetted amethyst.


Very thin, near transparent red hematite flecks inside a cabochon of Feldspar - Indian Sunstone.


Another Feldspar, this time Labradorite from Madagascar, with tiny black rods of Ilmenite - aligned in accordance with the structure of the feldspar.


More Hematite, This time developed as 'stringers' within a polished quartz from Brazil.


Ludwigite inclusions inside a facetted Peridot from Pakistan.




Two images of a Demantoid Garnet from Russia showing fine "Horse-tail" like fibres of "Byssolite" emanating from a tiny black chromite core.


Goethite sprays (commonly mistaken for Cacoxenite), forming shallow fans in layers in a pale amethyst from Brazil.
Notice the thin red flake of Hematite in the bottom right corner of the photograph.


Goethite again, this time forming a firework display inside a crystal of amethyst from the Tamil Nadu area of India.




Topaz From Brazil is the host in the two images above.
These inclusions have two immisible liquids and a central gas bubble.

Finally, a negative crystal found inside a quartz crystal from Pakistan.
This is a three phase inclusion (Solid, Liquid and Gas).
Trapped within the negative crystal is a gas bubble (most likely Methane) and the pale yellow liquid is natural oil similar in chemistry to Benzene. The solid black material is bituminous in nature.

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