Introduction
These layered rocks are schists and slates, interspersed with quartzites and abundant quartz veins. They form the largest geological outcrop in the area, including Montbaig and a smaller outcrop in Sant Boi de Llobregat.
They are metamorphic rocks formed from clays under high pressure and temperature around 300 million years ago. They are dark-coloured, unlike the lighter and more recent limestone of the Garraf massif.
Their layered structure is known as schistosity.
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