Gemology: P is for ...
Our gemology guide is back again with a look at gemstones beginning with P. In this article we invite you to discover pearl, peridot, petalite, phenakite, phosphophyllite, prosopite and pyrite. How many of those do you already know?
There are many different types of pearl; natural, shell, and artificial. Natural pearls are organic gemstones formed within the shells of molluscs and oysters and can be either freshwater or saltwater with sub-classifications according to wild-harvested or cultured (farmed), region (South Sea), and shape (button, round, mabe, baroque etc). We'll cover each of these variations as they occur in our gemology guide or specialist pearl guides. Natural pearls are formed when an irritant enters the shell (or is introduced in the case of cultured pearls), and the mollusc begins to coat the irritant in layer upon layer of nacre. The end result is a pearl that can be judged for quality on its shape, lustre and colour. Natural pearl colours can be white, ivory, cream, peachy-pink, lavender and black, which isn't technically 'black' at all, but rather a variety of shades including brown-black, green-black, purple-black and – the most popular one of all – peacock black, in which all the colours of the rainbow shimmer like oil on water. The different colours occur as a result of a number of factors including type of mollusc, water temperature, and the food source the mollusc consumes. Most genuine pearls on the market will be cultured pearls – only 1 in 1000-10,000 wild molluscs will contain a pearl, so that's a lot of pearl fishing! Shell pearls are artificially made from a mixture of ground mother-of-pearl (the lining of the shell), and a blend of binders and fillers. A tiny bead is repeatedly dipped into the mixture, dried and polished, until the desired size is reached. Shell pearls tend to be much heavier than natural pearls. Artificial pearls can be made from a variety of materials, generally glass, ceramic, resin or plastic, coated with a substance that will give the impression of a lustrous nacre. They're a lot quicker and cheaper to produce than cultured pearls!
Peridot is a beautiful yellow-green gemstone, and the birthstone for August! Peridot is the gem quality version of the mineral olivine, which forms deep below the earth's crust when magma cools. Most peridot at mineable depths made its way there in volcanic eruptions, as those living near the June 2018 eruption of Hawaii's Mount Kilauea are discovering. Peridot and olivine crystals have also been found in meteorites that scientists believe have come from an extinct planet that once orbited between Mars and Jupiter. Peridot looks stunning in jewellery, but it can scratch or chip easily and should be protected from extreme temperatures.
Petalite is a rare glass-like gemstone discovered in Sweden the 1700s. Crystals can grow fairly large and are often clear, though they also frequently occur in yellow, grey and pinkish tones. Although rare, deposits have been found in many corners of the world, including Western Australia. Petalite gemstones are often flawless, but with a hardness of around 6-6.5 on the MOHS scale and a tendency to be brittle, they are better suited to items of jewellery that don't get knocked, such as earrings or pendants. Petalite is also known as Castorite.
Phenakite / Phenacite
Phenakite can be considered more of a collector's gem than a gem used for jewellery. It's relatively rare and similar to quartz in appearance, occurring most often as a clear crystal but also occasionally in shades of pale yellow, grey and pink. When cut as a gem, good quality phenakite has a fire-like radiance similar to diamond. It's a hard gemstone well suited to jewellery, and we think it deserves to be far more well-known that it is!
Phosphophyllite Phosphophyllite is a crystal that forms in stunning shades of blue to sea green, but it is brittle in nature and so rarely cut as a gemstone as most collectors prefer not to risk their crystals by cutting them. Phosphophyllite was only discovered in 1920 (in Bavaria) and remains an elusive and rare gem.
Prosopite Prosopite is usually found as a dull powdery mineral, but a rare source in Mexico forms gems with a remarkable similarity to unmarked turquoise, thanks to the presence of copper. This Mexican prosopite looks beautiful when polished en cabochon, but is extremely hard to come by as most pieces belong to collectors.
Pyrite / Iron Pyrite Pyrite, also known as Fool's Gold, has a similar feel and gleam to solid gold, but gets its weight from its iron content. It's often found alongside gold (and can even contain up to 25% gold in its composition) so it's a good indication to prospectors that gold is nearby. Another nickname for pyrite is Devil's Dice because it forms in cubes or rhomboids, and although it has a golden glimmer it is also darkly streaked from the iron and sulphide. Pyrite can be used in jewellery, where it is more commonly called marcasite.
Image attributions: Petalite: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Phenakite: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Phosphophyllite: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Prosopite: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Pyrite: DerHexer, Wikimedia Commons, CC-by-sa 4.0 [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) or CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons
Next week: "How to Wear Your Clip-On Earrings" It's not as straightforward as you might think!