Paintbrush Agate Identification Guide

What Paintbrush Agate Looks Like

Paintbrush Agate is a type of plume or sagenite agate - translucent chalcedony hosting feathery, brushstroke-like mineral inclusions that appear to be painted or swept across the stone. The "bristles" are typically fine oxide or zeolite filaments (often manganese, iron, or celadonite) suspended in clear-to-milky silica. Background color ranges from colorless and gray to honey, tan, or bluish, while the plumes are commonly red, orange, brown, green, or black.

• Color: clear/gray/honey base with red, brown, green, or black plumes
• Transparency: translucent to semi-transparent
• Luster: waxy to glassy
• Habit: plume/sagenite inclusions in nodular or seam chalcedony

Step-by-Step Field ID Checklist

1. Look for brushstroke plumes that fan or sweep from a base point - the defining trait.
2. Confirm translucency. Light should pass through, revealing 3D inclusions.
3. Distinguish plumes from bands. Paintbrush is inclusion-driven, not concentric banding.
4. Hardness test. Scratches glass (Mohs ~7).
5. Inspect fracture. Conchoidal, glassy, no cleavage.
6. Acid test. No fizz.

Key Diagnostic Tests

• Mohs hardness: 6.5-7.
• Streak: white.
• Fracture: conchoidal; no cleavage.
• Acid: inert to dilute HCl.
• Density: ~2.6 g/cm3.

Common Look-Alikes and How to Tell Them Apart

• Dendritic Agate: dendrites are flat, tree- or fern-like 2D growths on a plane; paintbrush plumes are 3D, fuller, and brush-shaped.
• Moss Agate: has scattered moss-like clumps rather than directional brushstrokes.
• Plume Agate (general): paintbrush is a plume agate; the term emphasizes the linear, swept "brush" form.
• Flame/feather agate: flame patterns rise in pointed tongues; brush plumes are softer and fanned.
• Painted (dyed) agate: color is surface or crack-bound, not suspended inside clear silica.

Where It Is Found

Plume and paintbrush agates occur worldwide in volcanic and silica-rich sedimentary settings. Notable U.S. sources include Oregon (Priday/Graveyard Point area), Texas (Woodward Ranch and the Big Bend region), and various western desert localities, where plume agate formed in gas cavities and seams of volcanic rock.