Look for a natural octahedral or cubic crystal shape
Check for a rough, unpolished surface
Observe a greasy or waxy luster rather than a glassy shine
Note sharp edges and flat faces
Test for high hardness that scratches glass
Check for strong light refraction and sparkle under direct light
Look for a color range from colorless to yellow, brown, gray, or green
Compare weight to size; diamonds feel dense for their size
Examine for inclusions, fractures, or cloudy areas
Use a loupe to inspect for crystal growth patterns
Test thermal conductivity with a diamond tester
Verify that it does not have cleavage like softer minerals
Check for a hydrophobic surface that resists water
Compare against common lookalikes such as quartz, calcite, and glass
Have a gemologist confirm the identification