Gemstones Through Geological Time: 4.6 Billion Years of Earth's Natural Art
What do turquoise, dinosaur bone, petrified wood, and ancient bone have in common? Quite a bit of history, as it turns out.
When I'm working on a piece of rough stone, I'm usually thinking about its colors, patterns, hardness, and where to make that first cut. Sometimes I'm just hoping there's something interesting inside!
But I've also become fascinated with the history of the materials I work with. I've cut dinosaur bone, petrified wood, and fossil coral, and I've even used fossilized Stegodon bone beads in bracelets.
That got me thinking. Just how far back in time does this hobby take us?
I decided to create a geological time scale showing not just the familiar dinosaurs and other prehistoric life, but also the gemstones, fossils, and lapidary materials associated with different periods.
The result is my new poster, Gemstones Through Geological Time.
Not All Gemstones Have the Same Kind of History
One thing worth understanding is that the materials we work with have very different origins.
Organic gems come from living organisms or materials they produced. Amber began as tree resin, jet formed from ancient woody material, and pearls are produced by mollusks.
Fossil gemstones preserve evidence of ancient life. Petrified wood, fossilized dinosaur bone, fossil coral, and ammonites are some examples. Many can be cut and polished into beautiful cabochons.
Then there are mineral gemstones, such as turquoise, agate, jasper, and malachite. These formed through geological processes rather than directly from living organisms.
And here's something I hadn't given much thought to before: the age of a fossil isn't necessarily the age of the minerals that replaced it.
A Quick Trip Through 4.6 Billion Years
Let's start with the really old stuff.
Precambrian: Before Almost Everything
Long before dinosaurs, forests, or even complex animals, microorganisms were busy changing our planet.
Stromatolites are layered structures created through microbial activity, and some preserve evidence of life dating back billions of years.
Certain stromatolitic rocks can be polished, revealing beautiful layered patterns. Not bad for something that predates just about everything we recognize today!
Paleozoic: Ancient Oceans and Early Forests
The Paleozoic brought us trilobites, crinoids, corals, and straight-shelled nautiloid cephalopods.
Many of these fossils are found in limestone and other sedimentary rocks. Some make fascinating polished specimens, decorative pieces, and jewelry.
Later, extensive forests developed, eventually contributing to coal deposits and some of the petrified wood we find today.
Mesozoic: Dinosaurs and Some Wonderful Lapidary Material
Now we're getting into materials I particularly enjoy.
Dinosaur bone can become mineralized, sometimes with agate filling or replacing its original cellular structure. When polished, those cells can produce amazing patterns. Fossil dinosaur bone can also be fashioned into beads, cabochons, and other jewelry.
Then there's ammolite, the colorful gemstone formed from fossil ammonite shells, particularly those found in Alberta, Canada.
One unexpected benefit of creating this poster was learning about ammolite, a gemstone formed from ancient ammonite shells. I've seen plenty of ammonite fossils, but I hadn't realized some could produce such spectacular colors.
And of course, petrified wood. Some of the best-known material comes from the Triassic and Jurassic periods.
Imagine cutting into a piece of wood that's been buried for 200 million years and finding beautiful colors and patterns inside!
Cenozoic: Mammoths, Stegodons, and Amber
We're getting closer to the present, although we're still talking about millions of years.
Mammoths and Stegodons were ancient relatives of today's elephants. Their fossilized bones and preserved tusk material can be used for carvings, beads, and other decorative items.
I've made bracelets incorporating fossilized Stegodon bone beads, so I especially wanted to include this material on the poster.
Amber is another fascinating example. Baltic amber is primarily Eocene in age, dating back roughly 34–48 million years.
And occasionally, amber preserves insects or other small organisms, giving us an extraordinary glimpse into ancient ecosystems.
But Where Does Turquoise Fit?
You knew I couldn't write an article about gemstones without mentioning turquoise!
Unlike dinosaur bone or petrified wood, turquoise isn't tied to one particular geological period.
It forms through chemical reactions involving copper-bearing rocks, phosphorus, aluminum, and water, often in the weathered zones of copper deposits.
The turquoise itself may be much younger than the surrounding rock.
The same general idea applies to agate, jasper, quartz, and many other gemstones. They can form at different times wherever the right geological conditions exist.
Apparently, turquoise doesn't like being confined to just one era. I can relate. I don't particularly like being confined to just one type of stone either!
Putting It All Together
For the poster, I combined a geological time scale with illustrations of prehistoric life and examples of the stones and fossils associated with each period.
I also added a section at the bottom for familiar gemstones that can form across multiple geological periods.
It's not meant to be an exhaustive scientific reference. Think of it as a visual introduction to the connections between geological history and the materials we collect, cut, polish, and admire.
I made a couple of prints to share with fellow rockhounds at my gem and mineral club.
Every Stone Has a Story
That's one of the things I enjoy most about lapidary. You never quite know what you'll discover when you start cutting into a piece of rough material.
Sometimes it's a beautiful pattern. Sometimes it's an unexpected color. And sometimes it's a connection to an ancient ocean, a prehistoric forest, or an animal that lived millions of years ago.
Next time you pick up a piece of petrified wood, dinosaur bone, or fossil coral, think about just how long that material has been waiting for someone to appreciate it.
And to think, we may complain when a cabochon takes an extra bit of time to polish!
The Little Lapidary — Hand-crafted from rough to cabochon.