How to Identify Agate: What to Look For and Home Tests

These are quartz with crystals too small to see. They break with a curved, glassy fracture, scratch glass easily, and show color from trace minerals rather than from crystal faces. The properties that identify Agate — luster: A glossy, waxy appearance, especially on a chipped or broken surface; color: Mottled or banded; can be yellow, green, red, brown, blue, gray, or black. Lake Superior agates are mainly red, orange, and yellow, colored by iron oxide; cleavage or fracture: No cleavage (chalcedony); broken surfaces are smooth and glossy. For a rock, texture and grain size matter more than any single hardness number.

• Banding test: in fortification agate, each concentric band, when traced around an exposed face, connects back with itself — like the walls of a fort.
• Light test: agate is translucent and glows when held up to light.

• Jasper: Jasper is opaque, impure quartz, usually red, with no banding; agate is translucent with concentric banding.

Glacial action spread Lake Superior agates across Minnesota; commonly found in riverbanks, river mouths, gravel pits, and other exposed gravel areas.

Photograph a fresh, unweathered surface in daylight, then a second shot of any crystal faces or broken edge. Include a coin for scale. If you did a streak test, photograph the streak next to the specimen. The app suggests the likely mineral or rock; confirm with hardness and the tests above before you label it.