Agatized dinosaur bone is sort of like meteorite, it’s awesome just BECAUSE.
If you look at a cross section of a bone you’ll see holes. These are the places that used to house blood vessels and bone marrow.
Gem bone dealers call these spaces cells. And they are, in the sense of small enclosed places. What they are not is cells in the biological definition that involves nuclear material surrounded by a membrane or wall. Here we’re talking about seeing the larger structures formed by the bone cells.
Agatized dinosaur bone is the result of these empty places being replaced with mineral materials. The most common of these is chalcedony. Transparent chalcedony with patterns or banding is called agate, so dinosaur bones replaced with chalcedony are called agatized dinosaur bone, dino bone, or gem bone.
The largest gem bone deposits are in Utah and Colorado from the late Jurassic Morrison Formation. It is around 200-150 million years old and formed from silt and sand from flood plains.
There are a lot of variables to evaluating gem bone! There’s also a lot of division between what specimen collectors and jewelers will be looking for.
-Color. The brighter the better. Neutral colors are less in demand for collectors, though they work well for jewelers. Black is the most desirable for the cell outlines, followed by white, since both will give a dramatic contrast.
-Intensity. Again, the most intense, rich colors are generally the most in demand. Pastel colors are rare, so some prefer them. (I myself really like the hard to find delicate baby blue color.)
-Number of Colors. Apparently seven colors in one fossil is the least found and the most prized. I’ve never seen one like that in real life.
-Durability. Chalcedony is a fairly hard stone. Some of the other minerals found in gem bone-opal and calcite-are much softer, but calcite is supposed to improve the brightness of color and give the surface of the stone a silvery sheen. So again it depends on what it’ll be used for-a display piece needs less durability than a ring inlay.
-Cell Size. Generally the larger the better, so long as the contrast is good.
-Cell Pattern. There is a very rare fanning pattern only found in the vertebrae of some species, it’s generally a collectors only item since it’s considered too rare to cut up for jewelry.
-Type of Bone. For collectors the vertebrae with their unusual patterns, especially if they’re part of a pair. The ends of large bones are valued by both collectors and jewelers because they’re more likely to have large and well defined cells.
-Completeness of Bone. Again, for collectors. Complete bones are more valuable.
-Presence of Agate Fortifications. They sound to me like particularly beautiful castles, but apparently this is the proper term for the little crystal surprises you sometimes find in the bone. Sometimes fractures or large cells are filled with patterned agate, very rarely even amethyst or citrine crystals. Again, the larger and more unusual the better. I’ve only seen tiny white crystals in person.
-Treatment. Most of the agatized dinosaur bone in jewelry isn’t treated beyond the cutting and polishing. Sometimes cracks or holes will be filled with epoxy. Collector specimens require more treatment to stabilize them, since it’s a matter of keeping a whole piece rather than selecting the best part.
Most of the agatized dinosaur bone I’ve worked with is at the cut an polished level, but the bones inlaid with ammolite mosaic do have a coating. Ammolite is very thin and is often coated to give it a layer of protection. With these inlaid pieces the bone has been given the same coating as the ammolite so they have the same kind of sheen and look more of a piece.
Agatized dinosaur bone is pretty sturdy. But it’s still very old and best treated with care. It’s not a good idea to keep it in places that will get extremes of heat or cold-like a display case facing a window, wearing it into a sauna-or worse, a place that will go from one extreme to the other-like a car. It’s also best to remove any jewelry before swimming, chlorine compounds can bleach the ancient colors.
So they take a little extra care, like plenty of other fossils, but it’s DINOSAUR.