Black agate is a microcrystalline variety of quartz characterized by its opaque, deep black coloration often displaying subtle banding or concentric layers. It is frequently found filling cavities in volcanic rocks and is highly valued by lapidaries for its durability and smooth polish. When collecting, distinguish it from black onyx by its typically more chaotic or subtle color patterns compared to the distinct, uniform parallel bands of true onyx.
Is this black agate?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch black agate with a known reference. Black Agate sits at Mohs 6.5-7 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Black Agate leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Black Agate typically shows a waxy luster.
- 4Match the color rangeCompare against the expected color range: black, dark gray.
- 5Look at form & habitCrystal system: trigonal. Typical habit: microcrystalline, massive, banded.
Often confused with
Black Agate vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside black agate
Minerals reported to co-occur with black agate. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂
- Mohs hardness
- 6.5-7
- Density
- 2.6-2.7 g/cm³
- Streak
- White
- Luster
- Waxy
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Microcrystalline, Massive, Banded
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Jewelry, Collector, Decorative
- Host rock
- Volcanic Vesicles, Hydrothermal Veins, Geodes
- Typical price
- $5-50 for cabochons or polished slabs
Where rockhounds find black agate
2 mapped spotsClassic worldwide localities
- Brazil
- India
- United States
- Uruguay
- Mexico
Field-hunting tip
Look in volcanic vesicles, hydrothermal veins, geodes country — that is the host setting where black agate typically forms. If you start seeing quartz, chalcedony, calcite in float, you are in the right ground. Field specimens usually show a microcrystalline, massive, banded habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Oregon, Utah — start trip planning there.
Common questions
How do you identify black agate?+
Where is black agate found?+
Can I find black agate in the United States?+
How much is black agate worth?+
What rocks look like black agate?+
What minerals are found with black agate?+
What kind of rock does black agate form in?+
What is black agate used for?+
Find black agate on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
