This work is based on a petrography of gabbro. Gabbro is a dark-colored, coarse-grained, intrusive igneous rock that forms when basaltic magma cools slowly deep within the Earth’s crust. It is the plutonic equivalent of basalt, the volcanic rock that forms from the same magma but at the surface. Gabbro is composed primarily of calcic plagioclase and pyroxene, and may contain olivine.
In the Basque Country, gabbro outcrops are mainly located in the Urretxu quarry, in Gipuzkoa, and in the Aiako Harria massif (Peñas de Aya).
Location and Characteristics:
- Urretxu Quarry: This is a geological point of interest (LIG 40) where sills (tabular intrusions) of gabbro with a massive structure and even columnar jointing can be observed. There are quarries, both old and one large active one, that extract this material.
- Aiako Harria Massif (Peñas de Aya): This Paleozoic massif, one of the oldest materials of the Basque bedrock, contains gabbrodioritic enclaves and hybrid facies, the result of the mixing of basic and acidic magmas. The area surrounding the Aiako Harria Natural Park is of great geological and geotouristic interest.
Uses of Gabbro
- As aggregate and gravel for road construction and filling.
- As an ornamental rock (often marketed as “black granite”), it is used for kitchen countertops, tiles, and exterior and interior cladding due to its strength and ease of polishing.
