Arizona Ruby Identification Guide
Understand Arizona ruby, a misnomer for red pyrope garnet, and learn to identify it by color, hardness, single refraction, and how it differs from true ruby.
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What Arizona Ruby Looks Like
"Arizona ruby" is a historic misnomer, not true ruby (corundum), but red pyrope garnet from the American Southwest. The same chrome-rich pyrope is also sold as "ant hill garnet." It is a deep, slightly purplish to brownish red, glassy and transparent in gem grade, and usually occurs as small rounded grains or fragments weathered from volcanic (kimberlite/diatreme) host rocks. The color comes from chromium and iron.
- Color: deep red to purplish-red, sometimes with a brown or orange cast
- Luster: vitreous (glassy)
- Transparency: transparent to translucent
- Form: small rounded pebbles, broken fragments, occasional dodecahedral garnet crystals
- Size: typically small, often under a carat
Step-by-Step Field ID Checklist
- Recognize the name as garnet: treat "Arizona ruby" as pyrope garnet, not corundum.
- Check color in sunlight: a rich red with a slight purplish tone suggests chrome-pyrope.
- Test transparency and luster: gem material is clear and glassy.
- Confirm hardness: it scratches glass (7-7.5) but is softer than true ruby (9).
- Look for no cleavage: garnet breaks conchoidally with no flat cleavage planes; true ruby shows parting and a hexagonal habit.
Key Diagnostic Tests
- Mohs hardness: about 7 to 7.5 (true ruby is 9, much harder); a sapphire/ruby will scratch the garnet but not vice versa
- Streak: white
- Cleavage: none; conchoidal to uneven fracture
- Specific gravity: about 3.7 to 3.8 for pyrope (true ruby is ~4.0)
- Optical character: garnet is singly refractive (isotropic); ruby is doubly refractive with strong pleochroism, the most reliable separator
- Acid/magnetism: no acid reaction; not magnetic
Common Look-Alikes and How to Tell Them Apart
- True ruby (corundum): much harder (9), doubly refractive with pleochroism, denser (~4.0), and often shows hexagonal crystal form. "Arizona ruby" garnet is softer, singly refractive, and lighter.
- Almandine garnet: more brownish-red and slightly denser; pyrope ("Arizona ruby") is a purer, more purplish red.
- Red spinel: also singly refractive but with different inclusions and density; spinel forms octahedra.
- Carnelian/red glass: carnelian is softer chalcedony with waxy luster and only translucent; glass shows bubbles, lower hardness, and is singly refractive but warm to the touch and often with swirl/flow lines.
- Ant hill garnet: essentially the same material under a different name.
Where Arizona Ruby Is Typically Found
Arizona ruby (pyrope) weathers from kimberlite/diatreme rocks of the Colorado Plateau, particularly the Garnet Ridge and surrounding areas of northeastern Arizona (on the Navajo Nation) and adjacent Four Corners states. The grains are often concentrated in surface gravels and harvester-ant mounds, the same source as ant hill garnet. Collecting on tribal land requires permission.
Frequently asked questions
Is Arizona ruby a real ruby?
No. "Arizona ruby" is a misnomer for red pyrope garnet from the Southwest, not corundum. It can be distinguished from true ruby by its lower hardness (7-7.5 vs 9), single refraction, and lower density.
How can you tell Arizona ruby from a real ruby?
Real ruby is much harder (Mohs 9), doubly refractive with visible pleochroism, and denser (~4.0), while Arizona ruby (pyrope garnet) is softer, singly refractive (no pleochroism), and lighter (~3.7).
Is Arizona ruby the same as ant hill garnet?
Essentially yes. Both names refer to red chrome-pyrope garnet from the same Southwestern volcanic sources; ant hill garnet specifically describes stones gathered from harvester-ant mounds.
What does Arizona ruby look like?
It appears as small, glassy, deep purplish-red transparent grains or pebbles, usually under a carat, weathered from volcanic rocks and often found in desert surface gravels.