Organic Materials
Jet
Jet has no mineral chemistry to speak of — it's a genuinely organic material, a form of fossilized wood (most often ancient monkey puzzle-type trees) that's been compressed and chemically altered over millions of years under specific waterlogged, low-oxygen conditions, producing a lightweight, deep black material that takes an exceptionally fine polish and has been carved into jewelry for millennia.
The geology — what Jet actually is
- Mineral class
- Organic material (fossilized wood, a type of lignite/brown coal precursor)
- Chemical formula
- Predominantly carbon, with variable hydrocarbon content (not a fixed mineral formula)
- Crystal system
- Not applicable (amorphous organic material)
- Mohs hardness
- 2.5–4
What causes the color: Jet's deep black color comes from its high carbon content, the end result of ancient wood undergoing a specific type of decay and compression called coalification, under waterlogged conditions that prevented full decomposition and instead concentrated carbon within the material.
How it forms: Forms when driftwood or fallen trees, often from an extinct relative of the modern monkey puzzle tree, become buried in marine sediment and are compressed and chemically altered over millions of years under low-oxygen conditions — a process related to coal formation but distinct enough to produce jet's particular dense, carvable structure rather than ordinary coal.
- Whitby, North Yorkshire, England (the most famous historic source, especially prized during the Victorian era)
- Spain (notable historic source, particularly Asturias)
- United States (several minor deposits)
Treatments & imitations: Genuine jet is frequently imitated by black glass (French jet), vulcanized rubber, and black onyx or dyed black materials — all much more common in the market today than true fossil jet, given how limited genuine Whitby-quality material has become.
Real vs. fake: Genuine jet is notably light in weight for its size (a direct result of its organic, non-mineral composition) and feels warm rather than cool to the touch compared to glass or onyx imitations; it also produces a brown streak (rather than black) when scratched on unglazed porcelain, and can develop static electricity when rubbed, a property documented since antiquity.
The tradition — how people use Jet
Historical use: Jet has an exceptionally well-documented ornamental history — carved jet beads and amulets appear in Bronze Age British burials, Roman jewelry, and most famously in Victorian mourning jewelry, where Queen Victoria's extended public mourning for Prince Albert made polished jet the socially required material for formal grief jewelry across Britain for decades.
Metaphysical tradition: Modern crystal-healing tradition associates jet with protection and grounding, drawing on both its deep black color and its documented historical association with mourning and processing grief, discussed at more length above.
How to use it: Traditionally carved into beads, brooches, and mourning jewelry; modern use continues this pattern, with jet commonly worn as pendants and beads rather than set stones, given its relatively soft, carvable nature.
Cleansing & care: At Mohs 2.5–4, jet is soft and can scratch or crack under rough handling or sudden temperature changes; clean gently with a soft dry cloth rather than water or chemical cleaners, which can dull its polish over time.
Frequently asked questions
Is jet a mineral or a rock?
Neither, technically — it's an organic material, a form of fossilized wood chemically altered under specific waterlogged, low-oxygen conditions over millions of years, related to but distinct from ordinary coal.
How can you tell real jet from glass or plastic imitations?
Genuine jet is notably lightweight, feels warm rather than cool to the touch, and leaves a brown (not black) streak when scratched on unglazed porcelain — all properties that glass, rubber, and plastic imitations don't reliably replicate.
Related crystals
Black Tourmaline
Tourmaline Group
Black tourmaline, mineralogically called schorl, is the most common member of the tourmaline group — a complex family of boron silicate minerals — and it's genuinely one of the most abundant accessory minerals in granite and pegmatite worldwide, meaning the raw material is easy to source even though well-formed, lustrous crystal specimens are still selectively mined for the crystal and mineral-specimen trade rather than everyday construction material.
Black Onyx
Chalcedony Family
Almost none of the 'black onyx' sold in jewelry today is naturally solid black — genuine, fully natural black onyx is actually quite rare, and most commercial material is naturally grey or brown banded chalcedony that's been dyed jet black using a treatment process the ancient Romans themselves developed: soaking the porous stone in a sugar solution, then treating it with sulfuric acid, which carbonizes the sugar trapped inside the stone into permanent black carbon. It's one of the oldest continuously-used gem treatments in history, not a modern shortcut.
Obsidian
Volcanic Glass
Obsidian isn't technically a mineral at all — it's a mineraloid, volcanic glass that cools too fast for atoms to organize into any crystal structure, which is why it has no defined chemical formula and no Mohs-scale crystal system in the way quartz or feldspar do. That same rapid, structure-free cooling is what gives obsidian its razor-sharp conchoidal fracture, a property humans have exploited for stone tools and ceremonial blades for tens of thousands of years, right up through surgical scalpel blades used in some modern operating rooms today.
Where to buy Jet
We don't have an active affiliate program live yet, so instead of a placeholder link, here's the same buying guidance we'd give a friend.
Specialty mineral dealers & gem shows
The most reliable source for anything beyond common tumbled stones — sellers who specialize in minerals tend to disclose treatments and localities unprompted, because their repeat customers ask.
GIA/AGS-affiliated jewelers
For cut gemstones meant for jewelry (not raw specimens), a seller who can produce or reference an independent lab report (GIA, AGS) removes almost all of the real-vs-fake guesswork.
Marketplace sellers with a track record
Etsy and similar marketplaces host genuine small mineral dealers alongside mislabeled resin castings — check seller reviews specifically for photos of received items, not just star ratings.
Local rock & gem shops
Being able to handle a piece before buying lets you apply the weight and hardness checks described on each stone's own page — something no photo can substitute for.
Whichever seller you choose, ask directly whether the stone is natural or synthetic, and whether it's been treated (heated, dyed, irradiated) — a straightforward answer is the single best signal of a trustworthy seller, more useful than any star rating.
Some links on this page are affiliate links — if you buy through them, GemGlow may earn a small commission at no extra cost to you. We only link to sellers we'd genuinely recommend.
Sources and factual basis for the geology above: see our methodology.