Fascinating gem materials from prehistoric times
Your gorgeous gem set jewellery is more than a beautifully designed piece with a lovely pop of colour. It is a well thought out frame for exquisite materials created throughout the ages - gems formed over years under incredible conditions. The colourful crystals are brought to life at the hands of expert lapidaries to uncover their intrinsic beauty and often sparkle of the gem material. Their journey continues on to the hands of the maker who creates the final piece ready for it’s new life with you.
The better known gems like emeralds, rubies and sapphire are single crystals (fragments of a single crystal) that have been cut to maximize their colour and sparkle. But the field of "gemmology covers a vast range of other gem materials that are equally beautiful and even more interesting" says gemmologist Nicole van der Wolf. Take for example fossilized materials like dinosaur bone, fossil coral and agate druze she uses in her latest pieces.
Fossils are fascinating to a wide array of scientists including gemmologists. They teach us about early species, events in prehistoric times and understanding formation processes. Although fossils are found all around the world, not all are suitable for use in jewellery. Fossil material that is suitable for jewellery, is highly prized for its unique patterns and colour combinations.
How gem fossil forms
A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. The preservation process can take place in many ways, but most common for gem-grade fossil material is the replacement process also called permineralization or petrification.
The living things die and are buried quickly under sand, dirt, clay or ash sediments. Usually the soft parts decay, leaving the solid structure behind. Groundwater rich in minerals seeps in slowly and replaces the original organic tissues with agate, calcite or pyrite, forming a rock-like fossil. Pressure, heat, and chemical reaction cause the sediments to harden into a rock called sedimentary rock. This is the process that forms most bone, wood and coral fossils used as gem material.
Aside from their use in jewelry, scientists can use this type of specimen to perform research into the anatomic structure of ancient species. In recent years, several new species of saurids have been identified from mineralised dinosaur fossils, highlighting the importance of these specimens to science.
Agate geodes are not fossils as such, but form in a similar manner: air pockets in volcanic materials or cavities in sedimentary rock fill in over time with minerals from hydrothermal fluids or mineralised groundwater, leaving a hollow potato-like rock with a solid outer shell and inner cavity lined with the prized crystal druse.
When cut in half the outer solid edges show banding patterns and colours that indicate the varied stages of precipitation, reveal points of fluid entry into the cavity, and correspond to changes in chemistry. The crystal druse lining may be as coarse as large citrine or amethyst crystals to be cut into individual gems , or can be as delicate as a fine dusting of caster sugar on the inner surface.
Agatized fossil coral
Fossil coral is a natural gemstone that is created when prehistoric coral is gradually replaced with agate. Corals are marine animals and it is their skeletons that are fossilized and preserved. The fossil coral forms through hardened deposits left by silica-rich waters. The entire process can take over 20 million years.
Fossil coral should not be mistaken for endangered or protected reef coral or precious coral. Fossil coral is often used for the making of health and drug supplements because of their high calcium, potassium, magnesium and sodium content. Because fossil coral can remove chemical impurities such as chlorine and formaldehyde it is used in industrial fertilizers and water purification filters.
As a gem material it is prized for its interesting ancient coral patterns, most often appearing in flower shapes. The colours are due to the minerals and trace elements present in the silica-rich waters at formation. Fossil coral tends to come in neutral grey tones showing the coral structure, but some material is also colourful. The value of the gem material is determined by the clarity of the pattern, colour(s) present and translucency of the final gem.
Most gem grade fossil coral is found in Indonesia and in the USA in Florida and Georgia.
Agatized dinosaur bone
Agatized dinosaur bone used in jewelry is known as gem bone (or dinogem) and has been described as one of the most rare and beautiful fossils in the world. Specimens can be traced back to dinosaurs that roamed the earth during the late Jurassic Age around 150 million years ago.
The mineralized bone is formed when minerals from groundwater are deposited within the bone’s cells. In the most optimal of cases, the most delicate and minute details of the cellular structure of the original bone have been reproduced. The different colors and very unique pattern in gembone are caused by many minerals that enter the cells during formation, including agate, hematite, iron, pyrite, jasper, marcasite, quartz or other crystals.
A quick and easy way to spot authentic agatised dinosaur bone is the irregular surface of the polished gem. Due to the difference in hardness between the agate cells and the intricate bone structure, the polishing process recesses the structure whilst bringing a shine to the agate.
Highly agatized, beautifully colored and patterned dinosaur bone is almost only found in the Four Corners region of the Colorado Plateau in the USA (where the states of Arizona, New Mexico, Utah, and Colorado meet).
Druzy Quartz refers to a layer of minute quartz crystals that have crystallized on the surface of a quartz based mineral. It has a sugar-like appearance and is often found in the hollow cavity of agate geodes. Geodes look rather unassuming from the outside - not unlike a large potato. But the inside reveals unique banding of materials and colours and if we’re lucky an exquisite layer of sparkly druse.
Most druse is clear quartz that picks up colour from the underlying layers. For example black agate will show a fine black or grey layer of sparkly druze. Whereas iron tinted geodes will show a rusty-red body colour with a peachy layer of druse crystals.
The crystal layer may be as fine as caster sugar, or come in crystals large enough to cut into individual gems. The finer druse gives a magical snow-like sparkle, whereas the coarser crystals are more about colour and texture.
Large geodes may contain large crystals made of purple amethyst or golden yellow citrine that are large enough to be cut into individual gems. Or simply be displayed as sculpture for its own intrinsic beauty.
There is no easy way of telling what the inside of a geode holds until it is cut open or broken apart. Typically cut into flat surfaces of druse, a creative lapidary will examine the internal forms of the geode and create an unique gem that respects the amazing works of mother nature.
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A few words about caring for your gemsYour fossil gem may have survived for millions of years, but it's not immune to damage. Here are a few tips for keeping it looking beautiful:
Because fossil materials are a form of quartz (agate), it is quite durable.
Clean using warm, soapy water and a soft cloth, then rinse well to remove any soapy residue.
Despite its hardness and durability, fossil quartz can still be easily scratched by other materials. Avoid wearing, mixing or storing fossil quartz with other gems, whether softer or harder, to prevent scratches and fractures.
When storing fossil coral, wrap it using a soft cloth and place it inside a fabric-lined box for added protection.
Always remove gems and jewelry before exercising or any vigorous activity - knocks and excess pressure can damage any gem set jewellery. And like most gemstones, avoid the use of any harsh household chemicals (bleach, sulfuric acid and similar).