How to Tell the Difference Between Black Minerals and Gemstones

Many black minerals look similar at first glance, but they are formed in very different ways and have distinct physical characteristics. This guide explains how to tell the difference between commonly confused black stones, including Black Tourmaline, Obsidian, Jet, and other dark minerals, using clear, practical identification features.

Black Tourmaline (Schorl)

Formation

A crystalline boron silicate mineral formed in pegmatite and metamorphic rocks.

Physical Characteristics

• Deep black colour

• Distinct vertical striations (lengthwise grooves)

• Rough, ridged surface in raw form

• Moderate to heavy weight

How to Identify It

• Visible linear grooves along the length of the crystal

• Breaks unevenly rather than smoothly

• Rarely fully smooth unless polished

Black Obsidian

Formation

Natural volcanic glass formed from rapidly cooled lava.

Physical Characteristics

• Uniform black colour

• Highly glassy and reflective surface

• Smooth texture

• Conchoidal (curved, shell-like) fracture

How to Identify It

• Sharp edges when broken

• Mirror-like shine

• Looks similar to black glass

Jet

Formation

A type of fossilised wood derived from ancient tree material.

Physical Characteristics

• Deep black to brown-black

• Very lightweight compared to other black stones

• Dull to silky lustre

• Warm to the touch

How to Identify It

• Much lighter than expected

• Can leave a brown streak on unglazed ceramic

• Easily carved

Onyx

Formation

A banded variety of chalcedony (microcrystalline quartz).

Physical Characteristics

• Solid black or banded black and white

• Smooth, polished surface

• Slight translucency at thin edges

How to Identify It

• Uniform colour (often dyed)

• Does not show striations

• Less reflective than obsidian

Hematite (Polished)

Formation

An iron oxide mineral.

Physical Characteristics

• Dark grey to black appearance

• Metallic or mirror-like shine

• Very heavy for its size

How to Identify It

• Leaves a reddish-brown streak

• Feels noticeably dense

• Magnetic in some processed forms

Smoky Quartz (Dark Varieties)

Formation

A variety of quartz coloured by natural radiation.

Physical Characteristics

• Translucent grey to dark brown-black

• Glassy surface

• Internal fractures or inclusions

How to Identify It

• Light passes through thin edges

• Not fully opaque

• Colour appears smoky rather than solid black

Key Identification Tips

✔ Compare weight between stones
✔ Check surface texture under light
✔ Look for natural striations or fractures
✔ Examine edge translucency
✔ Avoid assuming colour alone is enough

Common Misidentifications

• Obsidian mistaken for Tourmaline

• Dyed Onyx sold as natural black stone

• Glass sold as Obsidian

• Jet confused with plastic due to weight