Jet, Whitby jet, onyx Obsidian & black agate

This section helps to distinguish the differences between Jet, Whitby jet onyx & Obsidian and offers tips on testing to identify

Whitby jet

Whitby Jet is a rare, organic gemstone made from fossilized driftwood. Found exclusively on the coastline of North Yorkshire, England, near the town of Whitby, it is famous for its intense, velvety black color and lightweight feel.

how to test to identify Whitby jet

To identify it, use the streak test—scraping the stone on unglazed ceramic will leave a brown or cinnamon mark, distinguishing it from coal, which leaves a black mark.

Whitby jet can easily be damaged if dropped on a hard surface and scratched by harder substances such as French jet so its good practice to store away from other jewellery.

Whitby jet can be cleaned and polished with a soft cloth and some toothpaste.

French jet

"French jet" (which is actually faceted black glass, not real jet) was introduced during the Victorian era to satisfy an overwhelming demand for black mourning jewelry when genuine Whitby jet became too expensive and scarce for the general public.

The Queen Victoria Effect
In 1861, Queen Victoria’s husband, Prince Albert, passed away. She entered a strict, decades-long period of mourning and wore exclusively black attire and jewelry. Because genuine jet was the stone of choice, the public quickly followed suit, causing demand to vastly outstrip the supply of real fossilized wood.

The Glass Alternative
To meet this massive demand and make mourning jewelry affordable for middle-class consumers, manufacturers (primarily in France and Austria) developed "French jet".

Cost and Mass Production: Unlike real jet, which had to be laboriously hand-carved, black glass could be pressed and molded into uniform shapes and beads, dropping the price dramatically.
Enhanced Shine: Faceted French jet caught and reflected the light, offering a brilliant, glittering appearance that organic real jet could not achieve.
The Weight: Surprisingly, the heavy feel of the glass became a selling point, as consumers associated its heft with value and quality.

Jet or French Jet is black glass it will test as glass on a gem tester

It is heavy and cold to the touch.

Onyx and obsidian

Obsidian (volcanic glass)

Obsidian is heavy and cold to the touch.

In UV blacklight it may look slightly brown swirls lines or layers may be visible .

Onyx

Onyx is a banded variety of chalcedony (a microcrystalline quartz) known for its parallel, contrasting layers of color, most commonly black and white, though it exists in red, brown, and green. It is a popular semi-precious stone used in jewelry, carvings, and luxury interior design due to its deep black color.

It will test as quarts on a gem tester.

You can find onyx that is completely black.

The primary difference between obsidian and onyx is their origin and composition. Obsidian is an amorphous, rapidly cooled volcanic glass rather than a true mineral, whereas onyx is a dense, crystalline mineral variety of chalcedony quartz formed by hydrothermal activity.

Black agate

Black agate is a grounding and protective variety of chalcedony (quartz) known for its deep color, glossy luster, and subtle natural banding. It is commonly used in jewelry and meditation items.

Black agate will test as quarts on a gem tester.

The difference between onyx and agate