Pliocene (5.3 to 2.58 million years ago), Pleistocene (2.58 million years ago and ending 11 700 years ago) and Holocene (11 700 years ago to the present day) sediments make up the bulk of the country’s surface. Our mountains – the heralds of magmatic activity – include Carboniferous, Permian, Mesozoic and Tertiary formations dating back to 358 million years to 2.58 million years.

The pre-Mesozoic (or Mesozoic) formations, older than 251.9 million years, are more likely to show mineral assemblages of a post-crystallization phase, associated with various ores. These include minerals such as fluorite (CaF2) or biotite.

The number of our minerals has increased significantly since the beginning of the Mesozoic era (251.9 million years to 66 million years). Examples are: Jurassic manganese (Mn), rhodochrosite (MnCO₃), or Triassic gypsum (CaSO₄·2H₂O), calcite (CaCO₃).

From the aspect of mineralogy, the most significant geological period is the Tertiary (66-2.58 million years ago), including the Miocene (23-5.3 million years ago) volcanic period.  Most of our region’s minerals were formed in this period, with the appearance of all varieties of quartz (quartz, amethyst, rock crystal, chalcedony, jasper, agate-pearls) and other minerals such as opals (wood opal, fire opal, liver opal, noble opal) or barite (BaSO₄). The majority of the Museum of Bihar’s natural history collection is from this geological period, mainly from the North Hungarian Mountains and the area enclosed by the current borders, but there are also finds from Transylvania, such as the opal varieties, the finds from Nagybánya (Baia Mare), and last but not least the famous minerals from Kapnikbánya (Cavnic).

Mineral is a solid, homogeneous, naturally occurring building block of the earth’s crust, with a distinct chemical composition and lattice structure, mostly crystalline, formed by geological processes, and in our country, extending to our historical borders, it has many species.