The Rice Northwest Museum of Rocks and Minerals in Hillsboro, Oregon, houses a world-class collection recognized as the finest in the Pacific Northwest and one of the finest in the United States. The Museum building, originally constructed as the private residence of Richard and Helen Rice, is listed in the National Register of Historic Places for its unique architectural style, natural stonework, and the extraordinary native Oregon woodwork found throughout the building.
One of the bedrooms in the house is now the Agate Gallery which features agates from Brazil, Mexico, and Argentina.
According to the Museum display:
“Polyhedroids are unusual geometric shaped agate/quartz found only in Paraiba state in northeastern Brazil. They were found in 1974 in reddish soil derived from decomposed basalt. The shapes do not match any known mineral but the triangular-shaped growth hillocks on their surface and the resulting shapes are consistent with the filling of spaces between intersecting blades of calcite called a ‘box work’ that later dissolved away.”