Lemon Opal Identification Guide
Identify lemon opal, a yellow common opal, and distinguish it from citrine, yellow chalcedony, and glass imitations.
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What Lemon Opal Looks Like
Lemon opal is a yellow variety of common opal, hydrated silica (SiO2 nH2O), with a fresh lemon-yellow to greenish-yellow body color. It is typically translucent to semi-opaque with a waxy to vitreous luster and a soft internal glow. Most lemon opal is plain-bodied without play-of-color, though some material shows mild opalescence. The color usually comes from finely dispersed iron or nickel. It is amorphous, so there are no crystal faces, and broken edges show smooth conchoidal surfaces.
Step-by-Step Field ID Checklist
- Assess color and glow. A clean lemon to yellow-green hue with a slightly milky internal glow points to common opal.
- Check luster. Waxy to glassy, softer-looking than faceted quartz.
- Look for play-of-color. Usually absent; vivid spectral flashes would mean precious opal.
- Examine translucency. Light passes through with a hazy quality at thin edges.
- Heft it. Opal feels light for its size.
Key Diagnostic Tests
- Hardness: Mohs ~5.5 to 6.5, softer than quartz; a hard steel file scratches it.
- Streak: White.
- Fracture: Conchoidal to uneven; no cleavage.
- Density: Low, ~1.9 to 2.2 g/cm3, distinctly light compared with quartz (~2.65).
- Acid: No reaction to HCl.
Common Look-Alikes and How to Tell Them Apart
- Citrine (yellow quartz): Crystalline, harder (Mohs 7), denser, and often shows hexagonal crystal form and stronger transparency; opal is softer and lighter with a waxier glow.
- Yellow chalcedony: Microcrystalline quartz, hardness 7 and density ~2.6, tougher and heavier than opal; chalcedony has a slightly waxy but denser feel.
- Yellow glass: Manufactured glass shows trapped round bubbles, mold seams, and often a colder, more even tint; opal has natural cloudiness and lower density.
- Lemon quartz (treated quartz): Bright greenish-yellow but crystalline quartz, hardness 7, transparent and faceted; clearly harder than opal.
Where Lemon Opal Is Typically Found
Lemon and yellow common opal form from silica-rich solutions in volcanic and sedimentary settings. Notable sources include Peru (Andean common opals), Mexico, parts of East Africa (Tanzania), and the western United States. Look for it filling seams and cavities in weathered or volcanic host rock.
Frequently asked questions
How can you tell if lemon opal is real?
Genuine lemon opal is hydrated silica: lightweight (density below about 2.2), hardness around 5.5 to 6.5, waxy to glassy luster, and translucent with a soft glow. It is clearly softer and lighter than citrine or yellow quartz and lacks the bubbles and mold seams of glass.
What is the difference between lemon opal and citrine?
Citrine is crystalline quartz with hardness 7, higher density, and often hexagonal crystals and bright transparency. Lemon opal is amorphous common opal, softer at 5.5 to 6.5, lighter, and has a waxy, glowing translucency rather than glassy clarity.
Does lemon opal have fire or play-of-color?
Most lemon opal is common opal with no play-of-color, just a uniform yellow body color. If a yellow opal shows vivid rainbow flashes it would be precious opal, which is uncommon in this color.
What gives lemon opal its yellow color?
The lemon to yellow-green color generally comes from finely dispersed iron oxides or trace nickel within the silica.