Water Opal Identification Guide

What Water Opal Looks Like

Water Opal (also called jelly opal) is highly transparent, nearly colorless opal, often with play-of-color that appears to float inside a clear, water-clear body.

• Color: colorless, water-clear, faintly grey, blue or yellow; when it shows fire, spectral flashes seem suspended in the clear stone.
• Luster: vitreous to glassy.
• Transparency: transparent, its defining feature (most opal is only translucent).
• Form: massive, glassy nodules and seam fillings; amorphous, never crystalline.

Step-by-Step Field Checklist

1. Check transparency. Water Opal is see-through, like clear jelly or glass.
2. Tilt for floating fire. Any play-of-color appears to drift within the body rather than on a colored background.
3. Heft the piece. Opal is light (SG ~2.0-2.2), lighter than quartz or glass of the same size.
4. Test hardness. Mohs 5.5-6.5; a quartz point scratches it (quartz won't be scratched by a quartz point).
5. Look for conchoidal fracture on edges.

Key Diagnostic Tests

• Mohs hardness: 5.5-6.5 (softer than quartz at 7).
• Streak: white.
• Cleavage/Fracture: none; conchoidal.
• Density: low, ~2.0-2.2 g/cm3, diagnostic lightness.
• Acid: no reaction.
• UV: hyalite-type opal can fluoresce bright green under UV (uranyl), a strong confirming sign for that subtype.

Common Look-Alikes

• Clear quartz/rock crystal: harder (7), denser (2.65), forms hexagonal crystals, no play-of-color; a quartz point will not scratch quartz but will scratch opal.
• Glass: often has gas bubbles, can be molded, and lacks genuine opal play-of-color; density and warmth differ.
• Hyalite opal: actually a type of water opal, glassy, botryoidal, often UV-fluorescent green.
• Girasol/clear chalcedony: chalcedony is harder (7) and waxier; girasol quartz shows a bluish billowy sheen rather than spectral fire.

Where It Is Found

Water/jelly opal comes from Mexico (a classic source, alongside Mexican fire opal), Ethiopia, Brazil and elsewhere where silica gels fill volcanic cavities. Hyalite, a clear water-opal type, occurs as crusts on volcanic and pegmatitic rocks worldwide.