Stone Origins

These unique moonstone-like feldspars, known as anorthoclase, come exclusively from the Stettin pluton, a half-moon segment of an ancient volcano rim that eroded to its current state over a billion years. It is part of the Wausau Rock Complex in North-Central Wisconsin. This is the oldest rock body in the area and is especially rich in alkali elements like potassium and sodium. What remains today is the quiet, weathered heart of a structure exposed to many of nature's most extreme forces.

The main rock here is syenite, which looks similar to granite but contains little to no quartz and a lot of alkali feldspar. Over time, molten material forced its way through cracks in the rock, forming pegmatite dikes that cut across the original stone and created pockets where large crystals could grow. Some of these rocks are unusually low in silica and host rare and colorful minerals like nepheline, sodalite, and fayalite, along with sodium-rich amphiboles and pyroxenes. The area is also known for zircon, thorium minerals, and rare earth elements. For generations, collectors have come here for striking black crystals of arfvedsonite and bright green, radiating clusters of aegirine (also called acmite).

The moonstone-type material doesn’t come from the main syenite itself, but from those later pegmatite dikes. Pieces have been found in small pits and old quarries, as well as in nearby farm fields where weathering and freeze-thaw cycles slowly push the stone up to the surface. The Moonstone Gardens sit on top of a dozen of these veins, and two in particular produce the bluest, highest crystal content in the area.  Most rough pieces don’t look especially exciting at first — often just pale, blocky feldspar — but when you turn them in the light, a soft glow suddenly appears, revealing the classic moonstone shimmer.

That shimmer forms because of how the crystal cooled. When feldspar is hot, sodium and potassium can share the same crystal structure. As the rock cooled very slowly, below about 400°C, the structure tightened and those elements no longer fit comfortably together. Instead of staying blended, the mineral separated internally into thin layers of potassium feldspar and albite, a sodium feldspar. These layers can be thick enough to see, or so fine they’re microscopic. When they’re spaced just right, light scatters between them, creating the floating, silvery glow known as the moonstone effect, or schiller.

Technically speaking, true anorthoclase only remains a single, unmixed mineral if it cools very quickly, like in a lava flow. The Wausau material cooled slowly, so it’s actually an intergrown mixture rather than a pure mineral. The diverse host stones create diverse and stunning effects.  Whether its in a grey, orange, or brown setting, the blue shillae remains vibrant and stunning.  For collectors and crystal lovers alike, that slow transformation is exactly what makes it special — a stone shaped by time, change, and quiet internal re-balancing, with its beauty revealed only when the light meets it just right.