Pearls – the Birthstone of June

How can June nearly be over?! It was still snow outside like literally two months ago! We sort of skipped spring here in Sweden and went straight to scorching summer temperatures which was quite a chock for this gal here who isn’t built for such warm weather.

Anyway. June. A month which not only has one but TWO birthstones: moonstone and pearl, and today it will all be about the forever timeless pearl.

Freshwater pearl jewellery set in 14k gold fill.

“Pearls are always appropriate” – Jackie Kennedy

 Pearls are with no doubt the most timeless, classic and sophisticated gem out there. It is regarded as one of the true precious gemstones together with diamonds, rubies, sapphires and emeralds and might even be the best-loved gem of all time.

Top: simple baroque freshwater pearl pendant paired with a luxurious 14k gold fill chain with elongated links. Bottom: handknotted freshwater and baroque pearl necklace using white silk thread and finished with a modern and minimal sterling silver toggle clasp.

 

Pearls – the beautiful result of a defence mechanism

First things first, what is a pearl?

A pearl is in fact an organic gem that forms inside of a living saltwater or freshwater mollusk.

Pearls are made up of concentric layers of calcium carbonate, CaCO₃, either aragonite or a mixture of aragonite and calcite. The layers are held together by an organic horn-like compound called conchiolin. The combination of the two (calcium carbonate + conchiolin) is called nachre –  the stuff that makes up the beautifully iridescent mother-of-pearl.

Left: the calcium carbonate mineral aragonite, here in crystal form. Top right: natural pearls in cross section clearly showing their concentric rings all the way through to the center of the pearl. Bottom right: the beautiful iridescence of nachre – Mother of Pearl.

 

The formation of a pearl begins with an irritant inside of the mollusk. The irritant could be organic, a parasite or a tiny speck of sand that found its way inside.

As soon as an irritant settle on the soft tissue it gets enveloped by a pearl sac – a layer of mantle tissue cells which make up the protective membrane on the inside of the mollusk shells. The pearl sac acts as a defence mechanism which seals the irritant off from doing any harm and then nachre is secreted, layer by layer, slowly building up a pearl. Typically, the build-up of a naturally forming pearl takes a couple of years.

Pearl sacs that eventually will become full grown pearls.

 

Perfect shining little spheres of delight

Due to the unique conditions under which natural pearls form they come in a dazzling array of sizes, colours and shapes. Perfectly round ones are actually very rare.

Below I’ve listed some of the most basic shapes:

• Round
• Semi-round
• Button
• Drop
• Pear
• Oval
• Baroque
• Circled

Perfectly round pearls are the rarest and most valuable shape. Semi-rounds are often used in necklaces or in pieces where the shape of the pearl can be disguised to look lite it’s a perfectly round pearl. Button pearls are like a slightly flattened round pearl. Drop and pear-shaped pearls are sometimes referred to as teardrop pearls. Baroque pearls are often highly irregular with unique and interesting shapes. Circled pearls are characterized by concentric ridges, or rings, around the body of the pearl.

The many shapes of pearls. Bottom right from the left: circled, baroque, button, drop and round.

 

Natural vs. cultured pearls

Natural pearls are nearly 100% calcium carbonate and conchiolin (nachre) grown in concentric layers by mollusks in the wild with no human involvement. Natural pearls are actually incredibly rare, and in the past many hundreds of pearl oysters or mussels had to be gathered and opened, and thus killed, to find even one wild pearl. Their scarcity was the reason for their then extraordinarily high prices.

Today natural pearling is confined mostly to seas off Bahrain and Australia, and to spare any mollusks not carrying pearls all mollusks goes through an X-ray examination in order to reveal any hidden pearls within.

Left: antique natural pearl and 19ct gold necklace. Right: antique natural pearl necklace with diamond clasp.

 

Cultured pearls are formed in pearl farms, using human intervention as well as natural processes.

In the pearl farms, a tiny piece of mantle tissue from a donor mollusk is implanted into the recipient mollusk to kickstart the pearl-forming process. To get perfectly round pearls, they often use spherical beads of mother-of-pearl as the nucleus. The use of an implant like this enables cultured pearls to be harvested much faster, just after six months.

Top: pearl farming in Fiji. Bottom: pearl extraction process.

 

Cultured pearls can be distinguished from natural pearls by X-ray examination since their interior gives them away.

Since cultured pearls are often ‘preformed’ they tend to follow the shape of the implant. When a cultured pearl with a bead nucleus is X-rayed, it reveals a different structure to that of a natural pearl. A beaded cultured pearl shows a solid centre with no concentric growth rings, whereas a natural pearl shows concentric growth rings all throughout. Their interior is of course also visible if you cut the pearl in half.

Top: illustration of the difference in interior between a cultured and natural pearl. Bottom left: cultured pearl cut in half clearly lacking concentric rings. Bottom right: natural pearls in cross section with obvious concentric rings all the way to the center.

 

Pearls, pearls, pearls!

The vast majority of pearls sold today are cultured in pearl farms and comprises mainly of four types: akoya, South Sea, Tahitian and freshwater.

Akoya

Pinctada fucata (akoya pearl oyster)

• Introduced to the market in 1916 as the first ever spherical cultured pearl
• Bead and non-bead cultured
• Environment: pristine saltwater far from cities
• Location: Japan and China, larger sized pearls (≥ 8.5 mm) are generally from Japan
• Colours: white or cream, some with hints of pink or green
• Size: generally between 3-7mm but can occasionally reach 9-10mm

Top: a classic white pearl necklace made with akoya pearls. Bottom left: akoya pearl in her akoya oyster shell. Bottom right: the subtle overtones of the akoya pearls: silver, rose and cream.

 

South Sea

Pinctada maxima (silver- or gold-lipped pearl oyster)

• Culturing began: 1950s
• Bead and non-bead cultured
• Environment: saltwater
• Location: between the northern coast of Australia to the southern coast of Southeast Asia passing the Phillipines as well as Myanmar
• Colours: silver, white and golden
• Size: generally between 8-16mm but can very occasionally reach over 20mm

Left: golden South Sea pearls on top of the golden-lipped oyster shell. Right: the golden colour scheme of the South Sea pearl.

 

Tahitian pearls

Pinctada margaritifera (black-lipped pearl oyster)

• Culturing began: 1960s
• Bead and non-bead cultured
• Environment: tropical saltwater, preferably clean-water lagoons
• Location: French Polynesia
• Colours: eggplant purple, peacock green, metallic grey and greyish blue
• Size: generally between 7-12mm but can very occasionally reach over 16mm

Top left: baroque Tahitian pearls. Top right: beautiful Tahitian drop pearl pendants made by Malin Ivarsson. Bottom right: the many overtones of Tahitian pearls. Bottom left: a Tahitian pearl in the shell of a black-lipped oyster.

 

Freshwater pearls

Hyriopsis cumingii or hybrid

• Appeared on the market in 1971
• Bead and non-bead cultured
• Environment: freshwater, usually cultured in lakes and ponds
• Location: China, Japan and Tennessee, U.S.A.
• Occur in a wide range of sizes, shapes and colours

Top and bottom left: the many shapes and colours of freshwater pearls. Bottom right: each freshwater pearl oyster can grow several pearls at once, resulting in a high production and thus cheaper prize.

 

How to care for your pearls

Pearls are, due to their soft calcium carbonate mineralogy, unfortunately easily scratched. Therefore they need to be handled extra carefully, both when wearing and when storing them, in order to maintain their beauty.

A first rule of thumb when dressing is: pearls should be the last thing you put on and the first thing you take off. This rule can and should be applied to all kinds of gemstone jewellery to maintain their beauty.

Below is a few pointers to keep in mind for keeping your pearls looking shiny and new to last a lifetime.

Cleaning

• For routine care, after each wearing, wipe your pearls with a very soft and clean cloth to remove any residues from the skin.
• For occasional, thorough cleaning, use warm and soapy water . If the pearls are strung, be sure the silk is completely dry before wearing.

Storing

• Store pearls separately from gems and metal jewellery, which may scratch their surface. Instead, store them wrapped in a piece of silk or satin.
• Never store pearls in a plastic bag. Plastic can emit a chemical that will damage their surface. The same is true of cotton wool.
• Never store pearls in a well-sealed box for a long time. Like your skin, pearls need a little moisture so they will not dry out.

Wearing

• Pearls can be damaged by many chemicals and all acids. The list includes hair spray, perfume, cosmetics and even sweat. Always apply perfume, hair products and perfume before putting on your pearl jewellery. And remember, this can be applied to all gemstone jewellery.

. . . . . . . . . . . . . . . . . . . . . . . .

There, this post turned out quite long and I don’t blame you if you just skimmed it. But if you read the whole thing, THANK YOU!

The blog post about June’s second birthstone, the moonstone, need to unfortunately be postponed. I’m busy busy preparing for a rock and jewellery show that’s taking place in a month’s time, I hope you don’t mind. To see some behind the scenes on me hustling away you are more than welcome to stalk me on instagram 🙂

Until next time, I wish you a wonderful summer!

♥ Linda

Aquamarine – March Birthstone

It’s time to dig deep into the science of the gemstone aquamarine and its mineral family today. This post will definitely be more science-y than my last post about birthstones which was about the amethyst, which can be considered a fairly “simple” gemstone.

I’m so excited to teach you all about this pastel blue dream of a gemstone and its mineral family so let’s just dive right on in shall we!

The aqua stone

The name aquamarine came to surface in the early 18^th century and is derived from the latin aqua marina which literally means ‘seawater’ and is of course a reference to its sea-blue colour. The gem has been a popular talisman to wear by seafarers for centuries since it was said to protect them during their travels by sea, as well as from drowning and seasickness. I might test this theory for my next time on the sea since I get seasick very easily..

 

Delicate, minimal and everyday jewellery featuring aquamarines. Made by yours truly.

 

 

The beryl family

The gemstone aquamarine is one of 8 varieties within the popular beryl family, all of which are characterized by their specific colour, and I’m sure you have heard about most of them. Beryl is a mineral which is most commonly found in granitic* pegmatites** where it has been found in epic sizes several meters tall!

 

Left: giant beryl crystals found in 1928 at the Bumpus Quarry, Albany. Right: beryl crystal in quartz.

 

* The word ‘granitic’ is referred to its mineral composition, which in this case is composed of quartz, feldspar and mica, minerals that you would find in a common granite.

** Pegmatites are rock formations that form in the later stages of a granitic magma chamber’s crystallisation. Pegmatites are characterized by their larger crystal sizes which can be 2.5cm to several meters in size. The bigger crystal sizes within these rock formations is due to a very slow cooling process, which allows the crystals to grow BIG.

 

Top left: granite. Top right: pegmatite. Notice the hammer in the lower left corner for scale. Lower left: where pegmatites form relative to the granitic magma it originated from. Lower right: pegmatite intrusion covering a massive cliff face.

 

Beryl is a beryllium aluminium cyclosilicate mineral with the chemical formula Be₃Al₂(SiO₃)₆. To explain, cyclosilicate or ring silicate refer to the arrangement of the Si (silica) and O (oxygen) atoms within the crystal structure. When it comes to the beryl, these atoms are arranged in such a way that it gives the beryl crystal its characteristic hexagonal shape.

 

Left: the atomic arrangement in a cyclosilicate mineral. Blue spheres are oxygen (O) and red spheres are silica (Si). Right: the hexagonal shape of the beryl, aquamarine variety.

 

Beryl varieties

Pure beryl is colourless, but it is frequently tinted by impurities; possible colours are blue, green, yellow, pink and red. All of these colours represent one or two specific beryl varieties.

• Blue – aquamarine and maxixe
• Green – emerald
• Yellow – golden beryl and heliodor
• Pink – morganite
• Red – red beryl or bixbite
• White / colourless – goshenite

Aquamarine

Aquamarine is the blue or cyan variety of beryl and can be found at most localities which yield ordinary beryl. The deep blue version of aquamarine is called maxixe which is most commonly found in Madagascar. The pale blue colour of aquamarine is attributed to Fe²⁺ ions, whereas the deep blue colour of maxixe comes from when both Fe²⁺ and Fe³⁺ is present.

Advanced: The difference between the two Fe-ions is their oxidation state, which describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. If an ion looses an electron to another element in the compound it gets a higher positive charge, if it gains an electron it gets a lower positive charge. Conceptually, the oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic.

The largest gemstone quality aquamarine ever mined was found in Minas Gerais, Brazil, in 1910. It weighed over 110 kg and its dimensions were 48.5 cm long and 42 cm in diameter.

 

Aquamarine specimens. Left and right ones are from my own private collection.

 

Emerald

Emerald is, as most of you already know, the green variety of beryl. But spoilers, emerald is the birthstone of May which means it will have its very own blog post.

Golden beryl and heliodor

Golden beryl can vary in colour from pale yellow to a brilliant gold, with the colour being attributed to Fe³⁺ ions. The term “golden beryl” is sometimes synonymous with heliodor, but golden beryl refers to pure yellow or golden yellow shades, while heliodor refers to more greenish-yellow shades.

 

Left: heliodor and golden beryl beads in my own inventory. Note the slight difference in shade. Top right: heliodor. Lower right: golden beryl. 

 

 

Morganite

Morganite is a rather rare gem. It is the pink variety of beryl and is also known as “pink beryl”, “rose beryl”, “pink emerald” and “cesian beryl”. It can vary in shades from light pink to rose. Orange/yellow varieties of morganite can also be found and colour banding is quite common. The pink colour is attributed to Mn²⁺ ions.

Pink beryl of fine colour and good sizes was first discovered on an island on the coast of Madagascar in 1910. In 1989, one of the largest gem morganite specimens ever uncovered was found in Maine, US. The crystal was 23 cm (9 in) long and about 30 cm (12 in) across, and weighed just over 23 kg (50 pounds).

 

Left: morganite with intergrown tourmaline. Right: morganite beads from my own inventory.

 

Red beryl

Red beryl, or bixbite, is the very rare red variety of beryl. As with morganite, red beryl gets its colouration from Mn, but from Mn³⁺ ions and not Mn²⁺ ions as in the case of morganite. As of to date, red beryl has only been found within the United States. The greatest concentration of gem-grade red beryl comes from the Ruby-Violet Claim in the Wah Wah Mountains in mid-western Utah. Unlike most other beryl varities, red beryl is usually highly included.

While gem beryls are ordinarily found in pegmatites, red beryl occurs in topaz-bearing rhyolites. Rhyolite is a volcanic rock and can be considered as the extrusive equivalent to the plutonic granite rock. Red beryl is formed by crystallising under low pressure and high temperature along fractures or within near-surface cavities of the rhyolite.

 

Red beryl. Note the high amount of inclusions. Perfectly imperfect in my opinion!

 

Goshenite

Goshenite is the colourless beryl variety and its name originates from Goshen, Massachusetts, where it was first discovered. The gem value of goshenite is relatively low and it can be found to some extent in almost all beryl localities.

Since pure beryl is colourless, one would assume that goshenite is the purest of them all. However, this assumption may not always be true as there are several elements that can act as colour inhibitors in beryl.

 

Goshenite specimens. The one on the right features an intergrown tourmaline crystal and colour impurities.

 

That’s a wrap

I hope you found this post interesting, I at least had a lot of fun writing it and doing some research on this interesting and beautiful mineral family.

So, if you ever want to find your own aquamarines or any of the other beryl varieties, the first step is to find yourself some pegmatite outcrops.

Happy hunting!

Linda

 

 

The January birthstone – garnet

So, it’s been a few weeks since my last blog post. I wanted to publish this particular one a little earlier but life got in the way and I definitely under estimated how difficult it would be for me to try to explain all of these science terms in an easy and understandable way, haha! But hey, it’s still January so as I see it, I made it just in time!

Garnet and 14k gold fill jewellery from my birthstone collection.

Anyways, this is the first post of what will be a monthly series about birthstones. Each month I will write a post dedicated to its respective birthstone(s) and give you facts about its different properties (colour, shape, hardness), where it can be found and other interesting facts.

I’m going to let my inner geology nerd shine through in these posts which means they will be jam packed with science! But don’t worry I will try and make it fun, interesting and easy for you. My goal is to make you look at each gemstone in a completely new light.

The glorious garnet

January is of course dedicated to garnets, one of my favourite gemstones due to its beautiful colour diversity, well-developed crystal shapes and it’s geological importance (I’ll come back to that). And also, it’s my birthstone!

 

One of a kind grossular garnet earrings.

 

Garnets have been used as a gemstone since the Bronze Age due to its commonness, beauty and durability. The word garnet can be thought of as a combination of two old words: the 14^th-century English word gernet, which means ‘dark red’, and the Latin word granatus, from granum (‘grain, seed’). The second one is possibly a reference to pomum granatum (pomegranate) whose fruits contain abundant and vivid red seed covers, similar in colour to red garnet crystals.

Garnets me and my husband collected from the gold mine where we first met. These were lying in the granites surrounding the gold ore.

Garnets are common and widespread minerals and can be found all over the world. They are particularly abundant in metamorphic rocks. Metamorphic rocks are rocks that have been altered by high pressure and temperature during for example a collision that forms mountains and turns granites into gneisses or limestones into marbles.

Although garnets form in all of the colours of the rainbow, garnets are often easy to recognize because they are generally found as well-developed crystals in a cubic crystal form, usually occurring as dodecahedrons, trapezohedrons or a combination of the two. I know, I know, you have no clue what those words mean, but the picture below might do the trick.

The many looks of garnets. Top row: dodecahedron (far left) and dodecahedron + trapezohedron combinations. Bottow row: trapezohedron (far right) and trapezohedron + dodecahedron combinations.

The geological importance of garnets

Garnets are more than just beautiful, they play an important role for geologists trying to figure out the genesis of garnet-bearing rocks. Garnets work like record keepers, they store the conditions of which they were formed and altered in. This means that geologists can figure out the temperature and pressure and hence the depth of where a garnet-bearing rock originated. This particular science is called geothermobarometry and was one of my favourite subjects when studying geology! I felt like a detective, figuring out where a particular rock came from and what it had been through since its formation.

The many species of garnets

So, garnets come in a wide variety, can you guess how many garnet species there are? Fifteen! They all follow one general chemical formula: X₃Y₂Si₃O₁₂ , where X can be either calcium, ferrous iron, magnesium or manganese, and Y can be either aluminium, ferric iron, chromium, manganese, silicon, titanium, zirconium or vanadium.

The six largest and most common species are:

• Almandine Fe₃Al₂Si₃O₁₂
• Pyrope Mg₃Al₂Si₃O₁₂
• Spessartine Mn₃Al₂Si₃O₁₂
• Grossular Ca₃Al₂Si₃O₁₂
• Andradite Ca₃Fe₂Si₃O₁₂
• Uvavorite Ca₃Cr₂Si₃O₁₂

Now, this is where it gets complicated, so bear with me as I try to explain. These six garnets are known as end-members and can be divided into two groups. Each group consists of three garnets which simply put mixes with each other during crystallization in what is called solid solution series. This means that almandine (Fe) can mix with both pyrope (Mg) and spessartine (Mn) and grossular (Ca) can mix with both andradite (Fe) and uvavorite (Cr).

With mixing I mean that a garnet is never 100% purely an almandine (100% Fe) for example. There is always a little bit of pyrope (Mg) or spessartine (Mn) mixed in. The name an individual garnet specimen is given is based on the chemical composition and the element (Fe, Mg or Mn) that has the highest percentage.

So, for example, if a garnet is analysed having 80% Fe, 10% Mg and 10% Mn in its composition, that garnet would be classified as an almandine. If a garnet has 60% Mg, 30% Fe and 10% Mn in its composition, it would be classified as a pyrope. And so on. If you take a look at the triangle below though, you see that the mixing has its limits. The yellow area represents the area of all the observed compositions found in garnets. The limitations are due to elemental behaviour during crystallization. I will not go into this further because this is a whole other very complicated topic.

 

The pyralspite garnets solid solution series. Each point of the triangle is dedicated to one of the three end-members and the yellow area represents their mixing area.

How to distinguish between the 6 most common garnets species

Although you can’t be 100% sure of what type of garnet you are looking at without a chemical analysis done in a lab, there are some features you can use to at least narrow down your guesses. Its colour and where you found it can give you some clues. So if you have some garnets laying around at home that you’d like to try and classify, read on! Below follows some short descriptions for each (major) garnet species that might be able to help you out during your detective work.

 

My private collection of garnet crystals. From the left: hessonite, spessartine, spessartine, grossular, demantoid, chrome grossular and tsavorite.

 

Almandine is the most common garnet species and have that deep red colour which garnets most often are associated with. Almandine garnets can be found in granites as well as in metamorphic rocks like mica schists and gneisses.

Pyrope is a fun garnet species because this garnet is an indicator mineral for high-pressure rocks such as diamond-bearing kimberlites, which means that they are used in diamond prospecting! Pyrope normally varies in colour from deep red to black which can make it hard to distinguish from almandine. Rhodolite is a violet-red to pink hued variety of pyrope which chemically is a 2:1 mixture of pyrope and almandine. Colour change or blue garnet is another variety of pyrope which is a mix of pyrope and spessartine. This is the rarest type of garnet. Apart from being found in kimberlites it can also be found in volcanic rocks, which means rocks that have been ejected on to the surface during a volcanic eruption.

Spessartine is most commonly known for its beautiful orange-yellow colour which it gets from the manganese in its composition. Spessartines are mostly more or less orange but they can also be coloured red by substituting the manganese with iron. A vivid bright tangerine orange variety has the aptly name mandarin garnet. Gemstone quality spessartine is rare but is most often found in granite pegmatites.

Grossular garnet can be colourless all the way to black, but it got its name from the green variety which resembled the gooseberry (grossularia) in colour. Other grossular varieties like hessonite are cinnamon brown to orange-red in colour. Tsavorite is a variety which is vividly green in colour. Chrome grossular is a bright green variety, often mistaken for uvavorite. Grossular is commonly found in contact metamorphosed limestones.

Andradite may be red, yellow, brown, green or black. There are three recognized varieties of andradite garnets: topazolite, demantoid and melanite. Topazolite is golden-yellow to olive coloured. Demantoid is yellow-green to emerald-green and has been called the ‘emerald of the Urals’, it is one of the most prized garnet varieties. Melanite crystals are opaque and black. Andradite garnets are commonly found in contact-metamorphosed limestone and in mafic igneous rocks.

Uvavorite is a rather rare garnet species which is bright green in colour. Uvavorite crystals are brittle and almost always too small to be cut as gemstones. Some of the largest crystals come from Outokumpu, Finland. Uvavorite is found in chromium-bearing rocks such as serpentines.

That’s all folks

I hope you enjoyed my first more science-y blog post about garnets. I had a lot of fun writing it but I have to admit, it took me quite a while and I’m still not sure I managed to explain everything good enough. But I had a deadline to stick to and hopefully I will get better at explaining with each birthstone post I write!

If you liked this post or if you have any questions about anything, please leave a comment 🙂

/Linda