Agate
Last updated: April 2026
Banded chalcedony variety. Natural agate is typically grey-white with muted banding; vivid commercial colors (red, blue, green) are almost always dyed. Sub-varieties: dendritic agate (fern-like manganese oxide inclusions), moss agate (moss-like inclusions), fire agate (iridescent), and eye agate (concentric rings). Banding pattern is the primary visual identifier.
Agate has a specific gravity of 2.61 and a refractive index of 1.530–1.543, with a Mohs hardness of 6.5–7.0. It is aggregate.
Physical & Optical Properties
Related: Quartz Varieties
Key Differentiators
- Characteristic concentric or parallel banding in multiple colors — primary visual identifier
- Banding may be wavy, straight, or eye-like (eye agate)
- Waxy luster; hardness 6.5–7
- RI ~1.535 (aggregate reading); SG 2.58–2.64
- Most commercial agate is dyed — natural colors are typically grey-white, red-brown, or muted
Common Simulants
- Glass (banded): Mold-banding in glass is too regular; SG lower (~2.5); isotropic under polariscope; gas bubbles under loupe.
- Synthetic resin / plastic: Much lower SG (< 2.0); warm to touch; isotropic.
Commonly Confused With
Commonly confused with: Lapis Lazuli.
Treatments
- Dyed (extremely common — most commercial agate is dyed)
- Heat Treatment (enhances or alters color)
Price Context
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying an agate? GemID walks through these tests in order — RI, SG, fluorescence, and more.
Try GemID Free →Studying for the GIA, FGA, or FEEG practical? Agate is one of the 130 species in GemID’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
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