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FACETIPS – A GEM CUTTER’S NOTEBOOK

by
Duncan Miller


The faceting articles published over the past few years in the Mineral Chatter have been compiled into a single 128 page document, available for download for those interested in saving all the articles together. To download the pdf file click here.

A 29,18 ct cuprite from Onganja, Namibia, cut by Duncan Miller and now in a private collection in Germany.


Browsing Archive: May, 2010

Mineral of the Month - Hausmannite

Posted by Site Moderator Webmaster on Monday, May 24, 2010, In : Mineral of the Month 

Crystal system:             Tetragonal                               Hardness:          5.5

Density:                        4.7 - 4.84                                  Cleavage:         Perfect

Streak:                          Brown                                       Colour:             Black metallic

Occurrence: Occurs mainly in high temperature hydrothermal veins and in contact metamorphic deposits.

Habitat: Crystals are pseudo octahedral up to 7,5 cm.    Composition:    Mn2+ Mn3+2 O4


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Mineral of the Month - Vanadinite

Posted by Site Moderator Webmaster on Tuesday, May 11, 2010, In : Mineral of the Month 
Vanadinite belongs to the apatite group of phosphates and has the chemical formula Pb5(VO4)3Cl. It is one of the main industrial ores of the metal vanadium and a minor source of lead. It is an uncommon mineral, occurring as the result of chemical alterations to a pre-existing material. It is found in association with the lead sulfide, galena, as well as wulfenite, limonite, and barite. It was first discovered in 1801 in Mexico by the Spanish mineralogist Andres Manual del Rio, and was eventua...
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Pegmatites - Basic Info

Posted by Site Moderator Webmaster on Tuesday, May 11, 2010,

Pegmatites are dike-like bodies of large grained igneous rock, formed by the slow crystallization of highly volatile solutions, during the last phase of solidifying deep-seated granite magmas. The name comes from the Greek word “pegmos” meaning “coarse”, and refers to their large-sized crystals, which are mainly feldspar, quartz and mica.  Their origin begins when a huge mass of molten magma intrudes upwards through cooler surrounding country rock, a name given to all other rocks, whi...


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Blesberg – June 2009

Posted by Site Moderator Webmaster on Tuesday, May 11, 2010,
It was with much yawning that Brett and I piled into my parents’ car at 3 am on Good Friday, to begin our trek up to Swartkop Camp Site. One last goodbye to three extremely unhappy dogs, and we were on our way. We arrived in Springbok at ten, to meet up with the Harrisons at the Springbok Lodge for breakfast, and then a short side trip to Steinkopf to meet a new member, Fanie, and bring him with us for the weekend. On arrival at Swartkop we set up camp, and then spent the rest of the day pa...
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Old Cape Town Mines

Posted by Site Moderator Webmaster on Tuesday, May 11, 2010,
by Trevor Vaughan Jones

THE QUARRY ON SEAFORTH BEACH

One of the least known quarries of the Cape Peninsula, and not easy to spot, was worked on Seaforth beach in 1865, where granite was shaped on site to re-enforce the shaky foundation of Roman Rock lighthouse, built only a few years earlier in 1861.  This well known False Bay “landmark” (if one may call it that) is South Africa’s only lighthouse built on a rock at sea, which becomes visible at low tides.  It was quite an achievement to...


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Mineral of the Month – Epidote

Posted by Site Moderator Webmaster on Tuesday, May 11, 2010, In : Mineral of the Month 
Epidote is a hydrous calcium iron alumino-silicate of medium hardness, between 6 and 7 on Mohs’s scale, and found in distinctive yellowish-green (“pistachio”) tones that range to an almost black colour. It is a metamorphic mineral, named by Hauy in 1801 from a Greek word “epidosis” meaning “addition”, because it was found to be an additional new mineral, and not a variety of tourmaline which it sometimes resembles, and until then what it was thought to be.  Its crystals are rath...
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