Purple Opal Identification Guide
Identify purple opal (such as Mexican Morado opal) by its waxy luster, lower hardness, light density, and conchoidal fracture.
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What Purple Opal Looks Like
Purple Opal is a hydrated silica (SiO2·nH2O), most familiar as the Morado opal of Mexico, where purple to lilac coloration is produced by fluorite inclusions in common opal. It is usually a common (non-precious) opal, meaning it shows no play of color; instead it presents a solid purple, lilac, or mottled body, sometimes with white or gray matrix. The luster is waxy to resinous, and it ranges from translucent to opaque.
Step-by-Step Field ID Checklist
- Luster: Note a waxy, resinous, slightly greasy sheen rather than glassy.
- Hardness test: It is softer than quartz — quartz scratches it; it scratches glass only with difficulty (Mohs ~5.5–6.5).
- Heft: Opal is light in the hand (low density).
- Color/matrix: Look for even purple-lilac, often with white or gray host rock.
- Fracture: Confirm conchoidal fracture and no cleavage.
Key Diagnostic Tests
- Mohs hardness: 5.5–6.5 (softer than chalcedony/agate at 7).
- Streak: white.
- Cleavage: none; conchoidal fracture.
- Specific gravity: ~2.0–2.2 (light — lower than quartz ~2.65).
- Stability note: some Morado opal may fade or craze with strong sunlight/drying.
Common Look-Alikes and How to Tell Them Apart
- Purple chalcedony / agate: harder (Mohs 7) and denser, with a more vitreous-waxy look; opal is softer and lighter.
- Sugilite: harder (~6–6.5), more massive and richly violet, often with a more uniform "grape" tone.
- Charoite: fibrous, swirly, and chatoyant; purple opal is structureless and waxy.
- Lepidolite: micaceous and softer, with visible flaky cleavage; opal lacks cleavage.
The diagnostic combination is waxy luster + hardness 5.5–6.5 + low density + conchoidal fracture + no cleavage, distinguishing opal from harder quartz-family purples.
Where It Is Found
Purple opal occurs in volcanic and silica-rich sedimentary settings. The best-known source is Mexico (Morado opal), with additional purple common opal reported from Peru and other localities. Protect specimens from prolonged heat and direct sun to avoid crazing.
Frequently asked questions
What is purple opal (Morado opal)?
Purple opal, often called Morado opal from Mexico, is a common (non-precious) hydrated-silica opal colored purple to lilac by fluorite inclusions, with a waxy luster and no play of color.
How can you tell if it's real purple opal?
Real purple opal has a waxy luster, a hardness of about 5.5–6.5 (softer than quartz), low density (it feels light), conchoidal fracture, and no cleavage.
Purple opal vs purple chalcedony — how do they differ?
Purple chalcedony is harder (Mohs 7) and denser with a vitreous-waxy look, while purple opal is softer (5.5–6.5), lighter, and more resinous in luster.
Does purple opal fade?
Some purple opal, particularly Mexican Morado opal, can fade or craze with prolonged sun exposure or drying, so it is best kept out of strong heat and direct sunlight.
Purple Opal identified by the community
Recent Purple Opal specimens identified with Rock Identifier.
