July – December 2024 Volume 28 Number 6 - Gemmological Association of Australia

IN THIS ISSUE

July – December 2024 Volume 28 Number 6

ARTICLES

Figure 10. Authors Robin Hansen (left), Léonie Rennie (centre) and François Farges (right) holding MNHN 96.135, the Moissan model of The Sergio. Photo courtesy of Kaylee Hansen.

The Sergio: The Life and Times of the World’s Largest Carbonado Part 2

In Part One of this story of The Sergio, the world’s largest carbonado (Hansen et al., 2024), we referred to an article about black diamonds (Hansen and Rennie, 2022) in which we wrote briefly about the history of The Sergio...

Figure 2. Petrographic section of Carrara marble from the Apennine Mountains, Italy. Note the well-formed equigranular calcite crystals displaying high birefringence and twinning lamellae. Crossed polarized view FOV: 2mm. Photo courtesy of the author.

Calcite – An Unlikely Gemstone with a Legacy

The mineral calcite (CaCO3) has multiple properties and qualities that make it a material of significance. It has been an essential component in the construction of prisms used in a range of optical instruments, and it is much admired for...

Figure 1. The gold necklace with four colourless gemstones that was presented for valuation.

True Identity – a Colourless Conundrum

To identify colourless gemstones, I first screen with a Dr Watson. This is a box-like device that detects synthetic diamond using pulses of LWUV and SWUV radiation. It can test multi-stone pieces of jewellery at once with results recorded, via...

Figure 1. Copal specimen with eye visible inclusions. The position of the ant is arrowed.

Is it Copal or Amber?

A yellow-orange transparent resin specimen measuring 61 x 26 x 20mm and weighing 25.6g was purchased at a gem and mineral show in Perth, Western Australia. No geographic location information was given.