Stephanite Identification Guide

What Stephanite Looks Like

Stephanite is a silver antimony sulfide (Ag5SbS4) and an important silver ore. It is iron-black to dark lead-gray with a bright metallic luster on fresh surfaces that dulls to sooty black on tarnish. Crystals are short prismatic to tabular, often striated, and may form pseudohexagonal twins; more commonly it appears as massive, granular, or disseminated grains intergrown with other silver sulfides. It is opaque and quite soft.

Step-by-Step Field ID

1. Note the color and luster. Iron-black with a metallic shine on fresh breaks.
2. Test hardness. Very soft (Mohs 2-2.5); a copper coin or knife scratches it easily.
3. Check the streak. Iron-black to black streak on unglazed porcelain.
4. Weigh it in hand. Heavy for its size (SG ~6.2-6.4).
5. Look at the company it keeps. Found with acanthite, pyrargyrite, proustite, native silver, galena, and quartz in silver veins.

Key Diagnostic Tests

• Mohs hardness: 2-2.5, very soft.
• Streak: iron-black to black.
• Specific gravity: ~6.2-6.4, distinctly heavy.
• Luster: metallic, tarnishing dull/sooty.
• Fracture: subconchoidal to uneven, brittle; cleavage poor.
• Sectile test: soft enough to mark but brittle.

Common Look-Alikes

• Acanthite (silver glance): also black and soft but is markedly sectile (cuts like wax with a knife) and is even heavier (SG ~7.2); stephanite is more brittle and lighter.
• Pyrargyrite/proustite (ruby silvers): show deep red internal reflections and red to vermilion streaks, unlike stephanite's black streak.
• Tetrahedrite: harder (Mohs 3-4.5) and gives a brown to black streak; tends to form tetrahedral crystals.
• Galena: lead-gray with bright cubic cleavage and a gray streak; galena is harder to mistake because of its perfect cubic cleavage.

Where It Is Found

Stephanite occurs in low- to medium-temperature hydrothermal silver veins, often a late-stage mineral. Notable sources include the Comstock Lode (Nevada), Freiberg (Saxony, Germany), the Erzgebirge, Mexico (Guanajuato, Zacatecas), and Cornwall (England).