Distinguish jet from black onyx [Was: Gaget...The Coal We Wear]

so… how does one distinguish jet from black onyx? I
remember my grandmother, who was in mourning for her husband for
sixty years, wearing jet, but it never occurred to me it was
different from what I see around now. Is there a way to tell?
thanks! ryr

Heft is a good one, luster is another and under magnification
they look very different. plus, jet gives off a distinctive odor
from a hot point.


Jet is very soft. About the hardness of amber. It is also very light weight.

Steven Brixner - Jewelry Designer - San Diego CA USA

RYR, Heat a needle til the tip is red hot and touch to some inconspicuous point on
the piece. If you get a little puff of smoke (it has a chemical smell) then it’s
jet…black onyx, no smoke, no smell. Jerry in Kodiak

If you ever put the two together it is easy, black onyx is much
harder and will almost certainly have a much better polish, it is
agate after all. Jet rarely (IMHO) takes better than a satin
finish, is much softer (Mohs 2.5 to 3) and so can be scratched by
a steel tool. Jet is also less dense so it will feel too light
for it’s size.

Andy Parker, Agate House Lapidary
Ulverston, Cumbria, England

Several years ago there was an article about jet jewelry in
Architecture Today, I think?- the article was very informative
about the sources of jet, the grades and the historical
importance. This type of ornament is assocciated with the
Victorian age and persons who live immediately after, it was the
choice of Queen Victoria after her beloved Albert died. It
reminds me of the hair broaches of the Civil War.

Lynn Wall Borzois of Legend stay cool in the hot summer

Hello RYR,

Jet is a fossilized wood, a form of brown coal.
- Refractive Index : 1.64 to 1.68
- Specific Gravity : 1.3 to 1.4
- Hardness : 2.5 to 4.0

“Black Onyx” is black stained chalcedony.
- Refractive Index : 1.53 to 1.54
- Specific Gravity : 2.58 to 2.64
- Hardness : 6.5

Hold a heated needle to a piece of jet, it will smell like
burning coal, the needle will have no effect on “black onyx”. Jet
will feel warm to the touch, “black onyx” will feel cold to the



Anybody try a scratch test? Choose a place not visible when set
and take a steel point and scratch lightly onyx won’t scratch…
Ringman John