Organic Gemstones and Other Interesting Classifications



We all know what gemstones are. They are the sparkly crystals made of minerals that are usually cut, polished, and set in jewelry. But what about opal? (not mineral) Or amber? (also not mineral) And what makes a stone precious or semi-precious? That’s what this post is all about—to answer your deep, burning questions.

Organic Gemstones

These are gemstones made from organic materials. (I know, you probably deduced that from the title but I wanted to write it anyway.) Some, like amber, pearl, and ivory are produced by organisms. Others, like petrified bone, have been mineralized, which means the organic matter has been wholly or partly converted into mineral (or some inorganic material). Most of you probably already know about pearls and amber (especially if you’ve been visiting this blog for awhile) but I hope to introduce you to a few new ones.

Fossilized Coral

Fossilized Coral

  • amber: fossilized resin that was secreted by ancient plants
  • ammolite: an extinct group of marine invertebrate animals that produced a chambered shell
  • bone: petrified bone, usually from dinosaurs; I’m adding petrified sand dollars here because it’s close enough
  • coral or fossilized coral: coral is a colonial organism that lives in warm, shallow marine waters; when used as a gemstone it’s the skeletal remains of coral polyps
  • fossil crinoidal: a fossilized marine animal (crinoid) that looks like a plant that’s embedded in limestone
  • fossil stromatolite or Mary Ellen jasper: a fossilized stromatolite (a structure created by trapping and layering biofilms of microorganisms) with red jasper and silver hematite
  • ivory: a hard, white material from animal tusks (traditionally elephant’s)
  • jet: a type of lignite, a precursor to coal
  • mother of pearl: when a pearl’s outer coating is made from layers of nacre, an organic-inorganic composite material that also makes the inner shell layer of mollusks (think abalone)
  • pearl: a hard mass that’s created inside the soft tissue of living bivalve mollusk
  • petrified palm or palm wood: fossilized parenchyma, the fibrous material of a palm tree found in the Oligocene-age sediments of the United States Gulf Coast
  • petrified wood: fossilized remains of terrestrial vegetation
  • turritella agate: formed from silicified, fossilized Elimia tenera shells (spiral-shaped shells) and found in a semitransparent agate


Non-crystalline Gems

These are inorganic non-crystalline gems referred to as mineraloids. They are mineral-like but have no crystallinity.

  • obsidian: volcanic glass
  • opal: a hydrated amorphous form of silica
  • moldavite: molten meteorite

⇒ Basically, if it’s pretty and can be used in jewelry, it’s a gemstone.

Precious and Semiprecious Gems

Fossilized Palm

Fossilized Palm

Precious stones are diamonds, rubies, sapphires, and emeralds. This classification goes back to the ancient Greeks. All other gemstones are considered semi-precious. However, different cultures make other distinctions. The terms have nothing (that I can see) to do with value. Some garnets cost more than diamonds! I suspect that the ancient cultures valued them for non-monetary reasons.

Diamonds vs Colored Stones

Gems are also divided into two categories: diamonds and colored stones. Diamonds are all diamonds and all other stones are everything else—regardless of color. A pink diamond is a diamond and a colorless topaz is a colored stone. This is basically because different cutting tools are required for the different stone categories.

Turritella Agate

Turritella Agate

First Water

I hadn’t heard of this classification before but apparently very transparent gems are considered “first water”, while “second” or “third water” gems are those of a lesser transparency. Crazy, right?

The 1753 edition of Chambers’ Encyclopedia states “The first water in Diamonds means the greatest purity and perfection of their complexion, which ought to be that of the clearest drop of water. When Diamonds fall short of this perfection, they are said to be of the second or third water, &c. till the stone may be properly called a coloured one.”

*Please note that the national and international trade in ivory of threatened species such as African and Asian elephants is illegal. (I know you probably know that too, but I had to say it anyway.)*

questionAny new gem stuff for you here? Got one to add?

Edited shortly after posting for because I missed the Non-crystalline Gems! ACK!
Share! It will make you happy, trust me.

While you’re here…

Sign up for my newsletter and I'll send you my Double Chocolate Chip Cookie recipe free. Other benefits include being the first to know exciting news, first to receive sneak peeks and sale information. Mailers are sparse.


  1. I didn't realize jet was an organic gemstone. Neat. Love that picture of fossilized coral!

    1. I didn't either but once I realized its source, it made sense. I love that picture too.

  2. I knew most were organic but not all. Funny how the diamond category is just diamonds.

    1. I didn't know all those were considered gems! LOL

  3. Hi Holly – all your series on gems are fascinating to read and I'm glad to know they are here … love the different variations on stones we can find – and I loved finding out more about First Water gems …cheers Hilary

  4. I have several ammolites from my father's rock collection. Also a ton of obsidian, both black and purple/clear.

    1. It sounds like a wonderful collection!

  5. Goodness, so many new facts and details. Pretty crazy how pink diamonds don't fall into the colored stones category. You'd think that's counter intuitive, but I suppose all sciences and categories have exceptions, eh?

  6. We have tons of obsidian here. My husband and I went to Glass Butte to dig for different kinds of it a few summers ago. I like that agate you picture. Cool.

  7. I remember having some kind of petrified wood as a kid, but I can't recall just what it was.

  8. Always love learning about gemstones. Some are just so beautiful.

  9. We are rock hounds. I'd love to get some ammolite. I think it's gorgeous.

  10. You started off with my favorite stone. I love amber. One of my favorite necklaces is from Turkey and they have some spectacular amber. There's a rich and exciting quality to that stone that I truly love. Less expensive than diamonds, but better than them in terms of interest. Diamonds are all hype and big money interests. Personal opinion.

  11. Interesting that precious stones aren't necessarily the most expensive – I tend to think of diamonds as the ones with the highest value.

  12. I have a piece of petrified wood that I inherited from my mom when she passed away. I don't know where she got it. But it's cool.

  13. For some reason, obsidian being a gemstone wasn't something that occurred to me. Huh. Very cool.

  14. Thanks for sharing this! Pearls and such are fairly self-explanatory, but I've always loved opal, and it never occurred to me to ask what it was. I would have never guessed that it was silica-based, like sand. 🙂

Comments are closed.

H.R. Sinclair © 2016
Scroll Up