Pyrite Crystal Form Series from Ambasaguas, Spain

This mounted crystal form series consists of four individually selected pyrite crystals from Ambasaguas in the Spanish region of La Rioja. The crystals are arranged on a transparent acrylic base and illustrate different morphological expressions between the pyritohedron and the cube.

From left to right, the series comprises a predominant pyritohedron, a pyritohedron-dominant combination form, a cube-dominant combination form, and a distinctly striated cube. Their joint presentation allows the differences in crystal habit, face development, and surface structure to be compared directly.

All four crystals were personally collected by the seller at the locality.

From Pyritohedron to Striated Cube

Pyrite crystallizes in the cubic crystal system and can develop several characteristic crystal forms. Alongside the cube, the pyritohedron, bounded by twelve pentagonal faces, is one of the best-known forms of this mineral.

Numerous combination crystals occur between these two ideal forms. Cube and pyritohedron faces are present simultaneously but developed to different degrees. This morphological variation is documented by the four crystals in the series:

1. Predominant pyritohedron
2. Pyritohedron-dominant combination form
3. Cube-dominant combination form
4. Striated cube

The arrangement does not represent a chronological growth sequence. Instead, it illustrates a morphological series composed of different crystals of the same mineral species and locality.

Selected According to Crystal Morphology

The crystals were not selected for uniform size but specifically for their individual morphology. During collecting at the locality, well-developed, nearly pure pyritohedra proved considerably less common than intermediate forms with varying proportions of cube and pyritohedron faces.

The first and slightly smaller crystal therefore documents the comparatively uncommon pyritohedral development. The two central crystals illustrate the transition between pyritohedron and cube, while the fourth crystal shows a nearly cubic habit with pronounced face striations.

Brass-Yellow Crystals with Metallic Luster

All four pyrite crystals display the mineral’s characteristic brass-yellow color and pronounced metallic luster. Differences in the orientation of the crystal faces cause individual areas to appear lighter or darker depending on the illumination.

Growth striations and irregular surface structures are visible on several faces. The striation is especially prominent on the cubic crystal at the end of the series.

The individual crystals measure between 1.8 and 2.2 cm and therefore belong to the thumbnail size category. The transparent acrylic base measures 10 × 5 × 2 cm.

Crystallographic Comparison and Collecting Piece

The particular appeal of this object lies in the deliberate combination of four different crystal forms. The labeled overview and the additional front and reverse views of the individual crystals allow their morphology to be compared in detail.

The pyrite series is suitable for systematic mineral collections as well as an educational object illustrating crystal morphology. At the same time, it documents the natural variety of pyrite forms found at a single Spanish locality.