We all know that gemstones are minerals and rocks, right? Wrong! As it often happens, some gemstones, despite their name, are not stones. Instead, these are the materials of biological origin that come from animals or plants and values for their rarity and appearance to the same extent as we value crystals.
Organic gemstones also include a group of valuable materials that are biological in origin but have been mineralized: biological materials have been replaced by opal, calcite, pyrite, or other mineral materials. Formally, it is no longer organic, but it is still unique as the organic structures, and internal shapes have been preserved. Leading examples are fossils of wood, coral, sea organisms, and bones.
Here we attempted to compile a full list of gemstones of organic origin. Most commonly known and widely used in jewelry and arts are pearl, mother of pearl, coral, amber, bone, and ivory. The extended list includes ammolite, ammonites, crinoids, dinosaur bone, fossilized coral and bryozoans, jet, mary ellen jasper, opalized wood, peanut wood, petrified wood, petrified palm, sand dollars, and turritella agates.
Amber is a variety of valuable fossilized resins of ancient coniferous plants. Its transparency and color vary, with most valuable varieties being highly transparent bright yellow, gold, or orange. Some Ambers also come in blue or black; the "youngest" ambers (a couple of million years) sometimes appearing green. It is remarkably light, can be burnt as an incense, and produces static electricity if rubbed against wool. Many ambers contain elements of prehistoric plants or insects.
Ammonite And Ammolite
Ammonites are fossilized chambered shells of extinct marine invertebrate, distant relatives of octopuses, and cuttlefish. Their shells can be used in decoration or elements of jewelry. Ammolite is a trading name used for the most valuable part of the shell: a fragile iridescent layer producing a spectacular play of intensely bright colors. The entire supply of ammolite comes from a single location in Canada.
Crinoids used to live at the bottom of the ocean. Even though they resembled stemmed plants, they were in fact invertebrates. Limestone and dolomite are where their fossils are typically found. The fossils can transform into some interesting gems once they are cut and polished.
Coral And Fossil Coral
Coral is an external skeletal shell structure built by colonial polyps similar to those living in warm, shallow marine waters and creating the reefs. The precious coral, however, comes mainly from several dark-loving species occupying deeper rocky plates and crevices. Valuable colors of the coral can be dark-red, orange-red, orange-pink, pink, white, blue, or black. Corals can be carved or even polished as used in their natural branch form.
Fossilized corals are corals of the ancient seas. They have been fossilized by changing the native calcium carbonate with calcite or quartz.
Although all dinosaur bones can be objects of curiosity and have a scientific value, not every dinosaur bone makes a gem. Dinosaur bone becomes a gem when the conditions allow for petrification, that is when organic materials undergo mineral replacement with chalcedony, pyrite, or quartz. The replacing minerals can sometimes be quite colorful, and the result of the petrification carries both the pattern of the structures of the initial organism and the qualities of the new mineral.
Mary Ellen Jasper
Mary Ellen Jasper is a mix of red jasper and silver hematite found in Mary Ellen Mine in Minnesota (hence the name). This gem is a fossil stromatolite, a layered structure created by ancient sediment-trapping microbial mats. Not only is this gem quite beautiful thanks to its dominant bright red color, but it is also incredibly ancient. The algae that created stromatolites in Mary Ellen dates two billion years back: long before any other plant or creature that we find in fossils inhabited Earth.
This fossil forms when wood material is buried for over a million years. Over time the substances dissolved in the groundwater slowly precipitates and infills the wood structures with silica, calcite, chalcedony, or other mineral material. Not all petrified wood is of gem quality, but many pieces are suitable for decorative purposes.
Petrified Palm is a state fossil of Lousiana. This fossilized material is commonly found in Oligocene-age sediments (between 20 - 40 million years ago). It differs from the petrified wood by the nature of the palm trees: it is fossilized parenchyma, fibrous material of which palm trees are made. It is not particularly expensive but can be polished into attractive lightweight brown "stones" with easily identifiable patterns. Fossilized palm roots can be particularly interesting because of their contrasting patterns.
"Peanut wood" is not really from peanuts: it is a variety of dark brown and black petrified wood with contrasting white patterns from which it got its name. Peanut wood is a fossil of driftwood that had been intensively drilled by a marine wood-boring clam called Teredo, and then sank to the bottom of the sea and had the resulting channels infilled with white radiolarian sediments. The typical age is around 120 million years old; Australia is known for some of the most exceptional finds.
Opalized wood is the rarest of all petrified woods and can be truly stunning. Some of the most famous examples of the opalized wood come from the species of Herringbone Sequoia. This wood underwent fossilization with the common opal lending it the attractive flash of colors intermixed with the dark "woody" elements.
The queen of gemstones is a softly glowing or iridescent organic gem produced by mollusks and several other groups of shellfish. Pearls are undoubtedly the most important of all organic gems. Pearls have been appreciated for over 6,000 years. Fragile and sensitive gemstone does not require any processing, and, unlike all other gemstones, can be cultivated.
Mother of Pearl
Often marketed as "MOP," is the thin iridescent and rainbow-colored nacreous layer of a mollusk shell. Some types of Mother of Pearl are more striking and more valuable than others, notably the abalone shells. Tridachna Gigas shell deserves a special mention, although it cannot be classified as a MOP: Chinese jewelers call it "the whitest of all gemstones." It produces enormous "pearls" that look nothing like other pearls we know because they do not have luster, but the sheer size of it makes it valued by collectors.
Ivory is convincingly the most controversial of all the gems on our list. It is made from the elephant tusks but also from the teeth of other large mammals such as walrus, hippopotamus, and even wild boar. Most countries in the world now either heavily restrict or completely ban the import and sale of ivory. The reason behind this is that hunting elephants for their tusks almost drove these animals to extinction not so long ago.
This rolling name was given to this agatized fossil by mistake. What was known as "Turritella" for several decades is a dark brown or greyish gem material containing obviously visible spiral fossil snail shells inside a semi-transparent agate body. Those shells were thought to belong to a genus of fossil snails Turritella. Still, later it was discovered that the correct snail species was "Elimia tenera," a member of the Pleuroceridae family. While the Turritella name remains, for now, the scientifically accurate one would be "Elimia Agate."
Jet is the gemstone that lent deep, impenetrable darkness its name: "jet-black."
Jet is a coalified wood, which forms differently from the normal coal. Most coal seams form when a buried ancient swamp with woody material undergoes degradation, heating, and pressure. Jet does not form in a seam. Jet can be created when an individual piece of wood from a half a dozen of species with suitable characteristics sinks to the bottom of the body of water and gets covered by organic-rich sediment. Compacted and heated in isolation inside an oils-rich shale, it absorbs the oil into its structures and transforms into a rock that is quite different from typical coal.