• Detail of a prehnite sphere, the surface composed of rectangular faces of the tops of crystals like a brick road. There are good epidote bow ties around the sphere, and a mix of epidote and light-colored crystals covering the surface.
  • A specimen with some roughly-formed epidote on a grainy rock matrix, and a large opaque sphere of prehnite.
  • Detail of the sphere
  • The bottom of the specimen, a broken surface of grainy rock matrix of light gray and green. The sphere is broken in cross-section, with some epidote with radial patterns to the left.
  • The back of the specimen, a grainy rock matrix mostly tinted green.
  • Detail of a roughly flat broken side of the piece, the radial pattern of the prehnite sphere apparent with a ring near the edge. There are radial and stacked epidote crystals to the left.
  • Detail of the broken side of the piece with a rough second partially-formed radial prehnite
  • Scale image of the specimen on a measuring mat, measuring about two and a half inches long and an inch and a half wide.
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Epidote with well-formed prehnite sphere

Epidote with well-formed prehnite sphere

$28.00 USD
$28.00 USD
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Locale: Imilchil, Midelt Province, Drâa-Tafilalet Region, Morocco

Approx dimensions: 2.5 x 1.5 x 1.25"

Approx weight: 115g


After some sleuthing on Mindat I was intrigued to discover the spherical formation on this specimen is prehnite. I actually didn't find one matching this specimen anywhere; all examples were translucent and not opaque. I suspect it could be a feldspar pseudomorph. Prehnite typically does not fluoresce—but this one does.

Prehnite and epidote commonly grow together because they have similar chemical requirements (both need calcium and aluminium, and often grow in hydrothermal environments). This is far from the version that comes to mind for most people. Prehnite is most frequently found as a translucent light green with a botryoidal habit, pierced by or growing alongside dark green crystals of epidote (like this). Instead this prehnite is an opaque sand-colored sphere formed of radiating crystals terminating in thin, rectangular ends. The sphere is fairly complete with one cleanly broken side revealing the radial growth pattern.

Epidote grows long slender prismatic crystals with saturated olive green color, though it can be more yellow, brown, or even so saturated it appears black. Radial growth forms are typical of the Imilchil region in Morocco. It’s common to find fans and bow-ties of epidote mixed in with individual crystals. This piece has several good bow-ties around the sphere. Epidote has a good luster which is apparent with the larger crystals on the specimen.

UV reactivity: the epidote is non-reactive but the prehnite sphere glows a light golden yellow in 365nm UV light.

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