THE AUSTRALIAN GEMMOLOGIST | Unusual Gem Minerals in Jewellery – A Dioptase Brooch
Unusual Gem Minerals in Jewellery – A Dioptase Brooch
Figure 1. Natural dioptase crystal cluster on calcite host from Tsumeb Mine, Namibia. Crystals show the typical high lustre and blue-green colour. Size: 34mm x 31mm x 28mm. Image courtesy of Lavinsky (2020).
Introduction
Natural, uncut, mineral crystals are often awe-inspiring as items of beauty. To the trained eye of a mineralogist or gemmologist, they are collector’s pieces; to a lapidary, they contain within them potential waiting to be uncovered by fashioning.
According to The Australian Museum website (Learn About Minerals, 2024), of the over 5800 known minerals, only about 100 are cut or otherwise modified, and only twenty are generally used in jewellery. Most gem material is faceted so the use of rough crystals in high-end jewellery is, therefore, uncommon. In recent years, there has been a resurgence in the use of uncut crystals as items of personal adornment, or as specimens for sculptural displays (see, for example, Gomelsky, 2021; Rice, 2022).
A quick internet search shows that many uncut crystals, including diamonds, are now used as the centrepiece in contemporary jewellery (Bjørnsten, 2020). Preserving the natural form of a crystal retains its association with its geological origin, especially if it is present with host material; this relationship is forfeited when a gem is faceted after which it has no observable connection with its geological (and frequently geographical) history. Knowledge of gemstone origin is becoming more important as increasingly consumers want to know how, and from where, specimens are sourced.
Dioptase Mineral
Not all gem crystals are suitable for faceting or fashioning, usually due to restrictions imposed by inherent physical properties including size, presence of cleavage planes or hardness. One example is dioptase, an uncommon copper-containing mineral whose crystals have a high lustre and show a vibrant, intense blue-green colour (Figure 1). Rarely found faceted over 1-2ct in size, dioptase is brittle, soft (5 on Mohs scale), and has perfect cleavage (see Table 1 for a list of properties and occurrences). Its use in jewellery is mostly limited to setting as a pendant or brooch (earrings too, but many natural specimens are too large and heavy). Their crystal clusters present a striking silhouette and texture, and large pieces make statement bespoke jewellery items. Whilst dioptase has historically been confused with emerald and has an appearance similar to uvarovite garnet in its drusy habit, dioptase specimens are stunning collector’s pieces in their own right.
Table 1. Mineral properties and characteristics of dioptase. Diagnostic gemmological constants SG, RI and birefringence, are in bold (GAA, 2024; Mindat, 2024; O’Donohue, 2006).
Dioptase Brooch
The brooch described here – which can also be worn as a pendant (Figure 2) – was purchased by the author through a local auction house several years ago. Captivated by the colour and its gemmological rarity, the author recognised the brooch as representative of the free expression quintessential of mid-20th Century jewellery style. The piece was made in 1973 and has a London assay mark (Figure 3; the maker’s mark and hallmarks are listed in Table 2). The design is bold and sculptural, typical of large pieces of jewellery that burst onto the jewellery scene in the 1960s and 1970s (see book reviews published in The Australian Gemmologist, 27(5), 2021, pp.295-297 for more on this topic).
The brooch is substantial in size (120mm x 47mm x 20mm) and weighs a hefty 65g. The gold lattice work below the setting around the dioptase is in two articulated sections which allow separate movement of the lower piece and of the narrow gold ‘tail’ when worn. The well-formed dioptase crystals are in their natural setting, formed as a druse (approximately 50mm x 40mm x 15mm), and have a layer of host quartz or calcite on the reverse. Magnification of a single dioptase crystal shows a distinct, euhedral, rhombohedral termination (Figure 4).
The setting is yellow gold, marked 14ct, and enhanced with fourteen brilliant cut diamonds totalling approximately 1ct which are scattered amongst the gold work. Typical of jewellery from this era, the diamonds are mere accessories to the main gem material. They are arranged so as to form part of the setting which hold but also embellish and highlight the dioptase crystal cluster, and are subtly incorporated into the overall design. The reverse of the piece has significant gold scaffolding (Figure 5). The style of the gold as freeform ribbons (both front and back) reflects the organic habit and natural undulations of the dioptase.
The dioptase specimen required considerable creativity and exemplary engineering skills by the maker in the construction of the unique setting. This piece is nothing short of flamboyant and demonstrates the status of jewellery as art.
Figure 2. Dioptase brooch/pendant set in 14ct gold with diamonds. Size: 120mm x 47mm x 20mm. Photo courtesy of the author.
Figure 3. Makers mark and hallmarks for fineness of gold, date letter and London on the reverse of the brooch. Magnification x45. Photo courtesy of the author.
Table 2. Hallmarks and makers’ mark for the dioptase brooch.
Figure 4. Single dioptase crystal showing typical euhedral rhombohedral termination. Magnification x45. Photo courtesy of the author.
Figure 5. Reverse aspect of the brooch showing the elaborate gold setting as well as the host material which supports the dioptase crystals. Photo courtesy of the author.
Famous Dioptase Jewellery
Andrew Grima, who was part of the mid-20th Century revolution in jewellery styles, favoured natural crystals and he typically mirrored the natural dioptase crystal habit in the setting or surrounding gold. Grima was very fond of dioptase and made several pieces during his lifetime which come to auction now and then, often selling for considerable sums of money. Grima Jewellery continues his tradition of bold jewellery with an abstract, organic aesthetic reminiscent of the styles he created in the 1960’s and 1970’s (Figure 6).
Figure 6. Dioptase pendant by Andrew Grima, 1973, part of his ‘Sticks and Stones’ collection, set with overlapping gold squares and princess cut diamonds. Photo courtesy of Roberts (2017).
Acknowledgement
Thank you to Susan Stocklmayer who, after seeing images of the brooch as part of a wider discussion we were having, suggested that I write this article. Susan also generously reviewed various drafts, particularly the mineralogical information.
References
Bjørnsten, M., 2020. Fine jewellery by Maya Bjørnsten, Rough Diamonds Jewellery. [online] Available at: <https://roughdiamondsjewellery.com/> [Accessed 23 April 2024].
GAA (Gemmological Association of Australia), 2024. Course Notes.
Gomelsky, V. (2021) New subscription service bridges gap between Gem and Mineral Worlds, JCK. [online] Available at: <https://www.jckonline.com/editorial-article/bridging-gap-between-gems-minerals/> [Accessed 22 April 2024].
Learn about minerals, 2024. The Australian Museum [online]
Available at: <https://australian.museum/publications/minerals/what-are-minerals/> [Accessed 21 April 2024].
Lavinsky, R., 2020. iRocks.com. [image] Available at:
<https://commons.wikimedia.org/wiki/File:Dioptase-195257.jpg>
[Accessed 21 April 2024].
Mindat, 2024. Dioptase [online] Available at: <https://www.mindat.org/min-1295.html> [Accessed 21 April 2024].
O’Donohue, M.,2006. Gems. 6th Edition. Oxford, Elsevier.
Rice, A., 2022. Raw Stone Jewelry Design and Care, International Gem Society.[online] Available at: <https://www.gemsociety.org/article/raw-stone-jewelry-design-care/> [Accessed 23 April 2024].
Roberts, C., 2017. Andrew Grima auction lures collectors with 55 jewels for sale. [online] Available at: <http://www.thejewelleryeditor.com/whats-on/auctions/andrew-grima-jewellery-auction-bonhams-london-top-lots/> [Accessed 22 April 2024].