Wavellite

Wavellite is a hydrated aluminum phosphate mineral that typically grows as radiating crystal sprays forming starburst-like spheres. Wavellite forms as a secondary phosphate mineral in low-temperature hydrothermal environments, often in fractures within aluminous, phosphatic rocks. It's particularly common in areas where phosphate-rich groundwater interacts with aluminum-bearing rocks.

The most distinctive feature is its radial crystal habit. Wavellite grows in spherical aggregates where needle-like crystals radiate outward from a central point like starburst fireworks. When these spheres are cut in cross-section, they reveal the beautiful radial pattern that makes wavellite one of the most visually striking of all minerals.

Arkansas produces the world's finest wavellite from the Ouachita Mountains region, where phosphate-rich solutions percolated through Paleozoic sedimentary rocks. The green color comes from trace amounts of iron and vanadium.

Wavellite's radial, starburst growth pattern is diagnostic. When hemispheres are broken or cut, the concentric and radiating structure is unmistakable. Green to yellow-green color, relatively low hardness (3.5), and association with phosphatic rocks are additional identifiers.

Distinguish from variscite (massive, lacks radial habit), malachite (botryoidal rather than radial, contains copper), and prehnite (different crystal system and habit). The radiating crystal pattern in cross-section is the most reliable identification feature.