Mexican Onyx is actually a banded form of calcite or travertine, not a true quartz-based onyx. It is prized by lapidary artists for its soft, pastel banding and translucent nature when sliced thin. It is commonly found in caves and near hot springs where it precipitates from calcium-rich water.
Is this mexican onyx?
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 mexican onyx with a known reference. Mexican Onyx sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Mexican Onyx leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Mexican Onyx typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, yellow, brown, green, banded.
- 5Look at form & habitCrystal system: trigonal. Typical habit: banded, massive, stalactitic.
Often confused with
Mexican Onyx vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside mexican onyx
Minerals reported to co-occur with mexican onyx. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaCO₃
- Mohs hardness
- 3
- Density
- 2.71 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Banded, Massive, Stalactitic
- Cleavage
- Perfect Rhombohedral
- Fluorescence
- Often Yellow or White Under SW UV
- Rarity
- Common
- Uses
- Decorative, Lapidary, Sculpture
- Host rock
- Limestone Caverns and Hot Spring Deposits
- Typical price
- $5-50 for decorative items
Where rockhounds find mexican onyx
1 mapped spotsClassic worldwide localities
- Tecali, Mexico
- Baja California, Mexico
- San Luis Potosí, Mexico
Field-hunting tip
Look in limestone caverns and hot spring deposits country — that is the host setting where mexican onyx typically forms. If you start seeing calcite, aragonite, dolomite in float, you are in the right ground. Field specimens usually show a banded, massive, stalactitic habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New Mexico — start trip planning there.
Common questions
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Find mexican onyx on the map
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