Mohs’ necklace

I've long been a fan of the Mohs scale of hardness, mostly because I just like how simple it is - 'this rock scratch that rock but that rock scratch this rock'. I also deeply appreciate the field kits, which have that classic nineteenth century natural sciences aesthetic. I've had a lot of time on my hands and been in need of a little distraction lately, so I decided to depict the scale as jewellery, using it as the basis for a necklace pattern and allowing me an excellent chance to sort out and use lots of different beads from my burgeoning collection/addiction.

I started a spreadsheet to help me organise and sort my beads, arranging them numerically based on the Mohs scale number for the gem, plus collecting interesting facts about them too. It’s been really absorbing to learn about what actually counts as a 'gem' or ‘gemstone’, the differences between minerals, rocks and mineraloids, the many mineral species, groups and series, as well as the organic gems with biogenic origins like pearl, shell, jet and amber.  

It's also fascinating how different sociological and historical, as well as geological, factors influence what we consider to be precious and rare, and what is merely a shiny rock!  In compiling all this info, I realised just how many of the world's wonderful shiny rocks I had not yet had a chance to get my hands and eyes on and have been happily hunting down and buying beads and cabochons online. 

Thankfully, a lot of gem beads are relatively inexpensive, and even for the precious stones, beads tend to be made of low-grade stones so it isn’t as expensive an undertaking as you might first think (and certainly cheaper than Warhammer) so as long as you don’t look too closely at my credit card statement, it’s all good.

Minerals, gem varieties and a golden heart

The necklace currently comprises 60 different gems; well, 58 recognisable gems and two mineral powders. The Mohs scale starts with talcum at number 1 and gypsum at number two, which are both far too fragile to use as beads, so I included them inside a gold-plated heart locket normally used for cremation ashes.

The rest of the scale is as follows: calcite at 3 (calcium carbonate - represented by limestone in the necklace), fluorite at 4, apatite at 5, orthoclase feldspar at 6 (represented in the necklace by moonstone), quartz at 7, topaz at 8, corundum at 9 and diamond at 10 on the scale.

In terms of gems represented, in total there are: 31 different individual mineral species, two mineral groups (garnet and tourmaline), six biological gems, one man-made glass (goldstone), three different types of rock, two mineraloids (snowflake obsidian and opal) and one element (carbon in the form of a tiiiiny diamond).

I have sometimes used more than one example of some minerals as many have different gem varieties which are known by different names. Notably, I have included thirteen different varieties of quartz. Quartz is the mineral silicon dioxide and the quartz group has many gem varieties, classified into cryptocrystalline (crystals not visible with optical microscopic) and macrocrystalline (crystals visible to naked eye).

I've included: amethyst, tiger's eye, citrine, aventurine, smoky quartz, rutilated quartz, tourmalinated quartz, 'strawberry' quartz (all macrocrystalline), and agate (banded and moss), jasper (red and zebra), onyx and carnelian (all cryptocrystalline).

There are also two varieties of beryl (emerald and aquamarine), three varieties of opal (precious, dendritic and pink) and both of the big corundums; ruby and sapphire. Interesting fact about corundum: it is a crystalline form of aluminium oxide, which can contain traces of iron, titanium, vanadium, and chromium, giving it a range of colours.

We use the term 'sapphire' to refer to all colours of corundum apart from red ones, which are termed 'ruby'. Sapphire alone tends to refer to blue varieties, with colours added to denote the others (yellow sapphire, pink sapphire etc), and where the line is drawn between a pink sapphire and a ruby is pretty subjective!

Fun facts to know and tell

Anyway, if you are interested in finding out more, I can highly recommend a couple of books on the subject: Precious by Helen Molesworth which is a really engaging look at gems through history, and The Natural History Museum Book of Gemstones: A concise reference guide, which is where I get most of my fun facts and has some beautiful photos.

I'm planning to add to the necklace over time and am currently on the lookout for andalusite, rhodochrosite and a couple more pretty varieties of beryl to round out my collection, like morganite and heliodor. Would also love any ideas you have, so please drop me a line if you have a shiny rock to suggest!