Did you know that Gemporia has its own museum? While many of our pieces, such as the world’s largest faceted Morganite, get plenty of attention on our television channels, some other pieces may be overlooked. So we’ve decided to shine a spotlight on some of our most fascinating but most underappreciated items, the mineral and fossil specimen collection.
I don’t know about you, but I really love mineral specimens. With their bright colours and otherworldly shapes, I find the plethora of ways in which crystals can grow a truly fascinating subject. With individual characteristics that are unique to each specimen, a mineral can tell you a whole world of information about the unique conditions in which it grew just by looking at its form. In the same way that our DNA carries all human history through time, each crystal carries its own creation story in its structure. From the tiniest of crystals to the most massive geodes, when you look at one of these forms, you are looking at one of the most extraordinary hidden worlds of Mother Nature’s creation. Here are some of the pieces in our mineral collection that I find most extraordinary.
Calcite is without doubt one of my absolute favourite minerals as it has such a fascinating history. It is the most stable form of calcium carbonate (CaCO3), and is a polymorph of Aragonite, meaning that they have the same chemical composition but a different crystal structure. Calcite is one of the most useful minerals on the planet, being used in the pharmaceutical industry, as well as being used in building. When it is opaque, it is one of the stones known as ‘marble’ or ‘alabaster’.
Transparent Calcite (sometimes known as ‘Iceland Spar’) is rarer and has some extraordinary properties. It is best known for showing very strong double refraction and demonstrating the polarisation of light. For this reason, it has been at the forefront of scientific studies on the nature of light. Christiaan Huygens and Isaac Newton both used Calcite samples to try to explain how light moves. Since then, Calcite has been used in lenses in photography, scientific instruments, measuring devices, prisms and gun sights, as well as modern experiments in the development of cloaking technology.
Famously, when the scientist René Just Haüy dropped a piece of Calcite onto his hard lab floor, it shattered into fragments of exactly the same rhombohedral shape. This led to the discovery of crystallography. As well as all of these impressive properties, Calcite can be fluorescent (glowing pink under long wave light and blue under short wave light), phosphorescent (glowing after exposure to daylight), thermoluminescent (glowing when heated) or triboluminescent (glowing when rubbed).
Our largest example of Calcite (the main specimen in the above image) is formed in an elongated pyramid with many blunt-shaped twinned crystals in a cluster known as a ‘nailhead spar’. There is also a polished rhomb with pyrite inclusions (the lower left piece), which due to the double refraction are impossible to count! There are also two smaller faceted pieces, (the lower centre and right piece) which are some of the most dispersive gemstones you will ever hope to see – only pipped to the post by Sphalerite, but leaving Diamonds and Zircon in their dust.
I love minerals that look weird! Aragonite definitely falls into this category. A close relative of Calcite, Aragonite is also made of calcium carbonate, but where Calcite has a trigonal crystal structure, Aragonite’s is orthorhombic. Aragonite forms under higher pressures than Calcite, and is less stable. After several millennia at atmospheric temperatures and pressures, Aragonite will alter to form Calcite.
Unusually, Aragonite can form through both chemical and biological processes – molluscs’ shells are made of Aragonite, as well as the endoskeletons of corals. The nacreous layer of Pearls and Ammolite is also usually Aragonite. As molluscs and corals fossilise, the Aragonite will gradually convert into Calcite. Aragonite crystals can grow in a number of shapes, including coralloidal (branched like a coral), prismatic, columnar, globular or as stalactites. They will also sometimes fluoresce pink, yellow, blue, green or white.
One of my favourite things about our Aragonite sample is how small it is. Barely 5cm at its widest point, its cluster of hexagonal columns jutting out at bizarre angles looks like a whole world of extraordinary beauty. This peculiar look is caused by multiple twinning planes – this is when crystals intergrow through each other. In a few species, such as Aragonite, crystals can grow as cyclic twins – a radiating pattern of growth.
Most of you will be familiar with Tourmaline. Technically speaking, it is a group comprising 33 minerals. Almost all gem-quality Tourmaline is from the species Elbaite – this covers all colours except Black Tourmaline, which is technically called Schorl. A member of the trigonal crystal system, Tourmaline crystals grow in long column shapes, which always make me think of sticks of rhubarb! One of the most amazing things about Tourmaline is how the crystals can change colour as they grow. This is due to the tiniest of changes in their chemical composition. This means that sometimes, across one gem you might see a stunning colour zoning known as ‘Watermelon’ or ‘Bi-Colour’.
This effect can be seen in our specimen, however ours is pink-red and Paraiba blue, making it an extremely rare example. In all, there are nine crystals growing through the 20x10cm Calcite matrix, but only two have been exposed. The clarity in the blue sections is also very good, so it is astonishing that this piece hasn’t been used for faceted gems. Luckily for us, however, it has not been used for jewellery and has pride of place in our museum.
Some of you may be familiar with Lepidolite – we are sometimes able to bring you cabochons of this gem set in jewellery. However, as you can see from this sample, it is astonishing that we are able to set this into jewellery at all. It is a member of the mica group of minerals, which are well known for growing in thin hexagonal sheets, often called “books”. With perfect cleavage, uneven fracture and variable hardness, this gem is every cutter’s nightmare.
Micas get their name from the Latin word 'mica', meaning ‘a crumb’ and 'micare', ‘to glitter’. This group tend to naturally be very reflective. Mica has plenty of applications in industry – it is used in paints and cosmetics to create a glittery effect. Lepidolite also tends to be slightly glittery and very reflective. Its colour can vary from silver to pink to yellow. Our museum specimen is a lovely shimmering lilac-grey tone with a pavement of hexagonal flakes catching the light and drawing the eye.
Cavansite is a perennial favourite of mine. Unusually, rather than being named after someone, Cavansite is named after its chemical composition – calcium vanadium silicate. It is a gorgeous, rich, bright blue colour. First discovered in Oregon in 1967, this rare mineral is a favourite among collectors for its incredible colour.
It grows in radiating rosette shapes from a central point. Although they are soft and brittle, a few lapidarists will cut them. When they are cut, however, they are equally striking. When well cut, there will be graining through the mineral, running to a central point. This always reminds me of the sun’s rays passing through water – if you’ve ever been diving, you’ll know what I mean! Seeming to travel into the distance, these are called ‘crepuscular rays’ and are caused by near-parallel shafts of sunlight converging on a point due to perspective. You can also see them between gaps in clouds. Often associated with God in antiquity, they always make me think of infinity. Cavansite feels to me like Mother Nature demonstrating infinity by etching it in solid form!
We’re lucky enough to have a few different Cavansite samples. The most interesting to see is it growing in situ on a crystal of stilbite, which is itself a beautiful sample, with ‘bow-tie’ twinning in some areas. There are also three pieces of Cavansite that have been carefully removed from their host – a radiating circle (the right faceted specimen, above), a segment of a larger circle (the centre piece) and most striking of all, a wonderful ‘wheat-sheaf’ form (on the left).
Geodes are hollows in rocks, in which crystals have grown. They are usually formed in gas bubbles in volcanic rocks, or where water has created voids in limestone. In May 2011, our CEO Steve Bennett visited the Amethyst mines of Rio Grande do Sul in Brazil. Brazil is well known for the quality of its geodes. Brazil isn’t on a fault line, meaning that there were long, stable periods for these geodes to grow, giving them a chance to form with great formation and clarity. Geodes are mined by boring into rock, then removing them from the ground and sawing them in two with a huge, rotating Diamond-tipped saw. If the crystals are patchy within, their interior will be reconstructed to some degree and the borehole filled. A layer of concrete may be added on the outside for stability and shaped so that it can stand upright, then the exterior is painted. While Steve was in Brazil, he bought two pairs of enormous geodes – an Amethyst pair that sit in our museum and a larger Citrine pair which sit in our Gemporia TV studio.
The most interesting of the pair is the shorter – the Amethyst geodes. Standing at around seven foot tall, this pair have a few inclusions. Three separate Calcite crystals several inches across have set up home within the geode. Miraculously, all three were left intact when the geodes were sawn open, one crystal having been missed by the tiniest of margins. Our Citrine pair is housed in our TV studio and is even taller, at over nine foot!
Trilobites were a group of arachnomorph arthropods. They are an extinct group, but their closest living relative is the horseshoe crab. Living underwater from the Early Cambrian (541 million years ago) to the Late Permian (252.2 million years ago) era, this diverse group of over 20,000 species tended to live on the sea bed as predators or scavengers, or swam, feeding on plankton. These creatures shed their exoskeletons as they grew (like modern-day crabs), so most trilobite fossils are a moulted shell, rather than the creature itself. Their body was segmented, allowing some varieties to curl up in a ball, like a modern woodlouse. It took a long time for trilobites to be properly understood, but they have been described in writings since antiquity. Ute Native Americans wore trilobite fossils as amulets and there is evidence to suggest they were also worn by prehistoric civilisations in the south of France. Trilobite fossils have been instrumental in our understanding of both evolutionary history and continental drift. Some of the best places in the world to find them include Dudley in the Midlands, Llandrindod Wells in Powys, or Millard County in Utah.
Our trilobite fossil is around eight inches long. Despite some cracking, the body segments are really easy to pick out. The weight of the sediment resting on the trilobite as it fossilised has caused its backbone to crush, with three segments having broken under the weight and one half has become slightly separate from the other.
More properly known as ‘Prasiolite’, this Green Quartz is incredibly striking. It’s depth of colour is extraordinary for its species. Prasiolite is named after the Greek words for ‘leek’ and ‘stone’. Now, you may rightly be thinking that this sample is less ‘leek green’ and more ‘fern green’. I was astonished when I discovered that this piece is natural.
Naturally green Quartz is rare in any case – more usually it is treated Amethyst. A Prasiolite with this depth of hue is extremely unusual – I’ve never seen anything else with its depth of colour. Green colouration in Quartz is usually caused by Fe2+ atoms. Then the crystal will need to be heated, either naturally or in a lab and/or exposed to radiation (natural or otherwise). To produce a green as dark as ours, I’m more inclined to think that it is coloured by something else, perhaps chlorite or fuschite. If it is coloured by fuschite that would technically make it Aventurine. However, Aventurine is usually opaque. The colour is clearly glorious, but I’m a little baffled by how it’s come about. Answers on a postcard!
In the Ordovician period (485.4 million years ago – 443.8 million years ago), the oceans were very different to today. Fish were slowly evolving, but most marine life was made up of molluscs and anthropods. Some of these varieties of molluscs were cephalopods. Today, there are around 800 species of cephalopod, including squids, octopuses and cuttlefish.
There are around 11,000 species that have become extinct. Among those is the Orthoceras. This nautiloid cephalopod takes its name from the Greek for ‘straight horn’ and was indigenous to Sweden and the Baltic states. They had a long, thin conical shell and a protruding tentacled head. As this cephalopod is fossilised, the soft parts are lost, leaving an impression of its shell in the rock.
Our example is around a foot tall and weighs over 5kg. Looking closely, it is possible to make out the siphuncles in the centre of the orthoceras. These siphuncle tubes ran along the length of the creature and could either fill with water, which would be pushed out to propel it through water, or filled with air as a buoyancy aid. There are nine large orthoceras in this example, but also a number of smaller ones in between, perhaps thirty or more.
QUARTZ WITH PYRITE
One of the most striking pieces in our museum is this Pyrite sample. You’d be forgiven for thinking that what you’re seeing here is a river of gold. It is actually iron Pyrite, otherwise known as ‘fool’s gold’. Visually, Pyrite and gold are very similar and despite often proving to be a disappointment for gold prospectors, was seen as a good omen, since it often signposted where gold might be found. Whereas gold is a noble metal, Pyrite is an iron sulphide and is chemically reactive. It was used in early firearms, as it can create a spark when struck against steel. Although both Pyrite and gold form in the cubic crystal system, they usually grow in different habits. Gold will often form in small grains within a host rock, or arborescent (‘tree-like’) growths, whereas Pyrite will usually form in perfect cubes, with shining surfaces, looking almost man-made. It can also form in radiating ‘suns’, flat circular disc-shaped crystals that are extremely reflective, formed along horizontal cracks in harder rocks. You might have noticed, however, that ours is neither a cube nor a disc, but rather what is called ‘massive’.
Looking at this sample, I think it may have been formed by volcanic action – the Quartz is mostly fine-grained and (for want of a better word) ‘messy’. To my eye, it looks as though the Pyrite has melted and solidified in this peculiar and eye-catching way. In our sample, the Quartz is a stripe within a piece of graphite with what seems to be a small Peridot crystal growing through it, which is definitely a sign that this sample is volcanic in origin.
ZINCOLIVENITE WITH SERPIERITE
You will be forgiven for having not heard of these minerals. They are not perfectly formed crystals, rather they have formed as most minerals do – as an aggregate. I’ll be honest with you – until I spotted this sample, I had never heard of Zincolivenite or Serpierite either! What drew my attention was the extremely vivid and saturated colour of both mineral species. It is also interesting to note that both of these minerals are rare, only occurring in a few of the same places. I have not been able to find another example of these minerals growing together in this way. The Turquoise-green mineral is Zincolivenite, a zinc-rich heavy member of the Olivenite group, which also contains Adamite, a firm favourite among our Gem Collector audience. Not to be confused with the Olivine family, Olivenite is also named after its colour. It is a soft mineral made up of zinc, copper and arsenic, which means it is sadly not suitable for jewellery. Its striking colour is caused by its copper content and traces of manganese and cobalt, creating a bright and vivid green that is truly spectacular.
Serpierite is the royal blue mineral. This brightly coloured mineral is a rare sulfate mineral, often created as a natural by-product of mining. Zincolivenite and Serpierite only occur in one place in the world together, where this sample originates, the ancient Lavrion Mines of Attiki, Greece. As far as we can discover, this is the only photographed example of these rare minerals side-by-side, making this an extremely rare specimen. The swirling, psychedelic patterns in this sample are particularly striking.
If you ever come on a tour of our building, you’ll be able to see these stunning crystals and many more for yourself in our museum. In the meantime, you can continue to build your jewellery and gemstone collection with us here.