This "speckled stone" is a sedimentary monomineralic rock, meaning that it is formed of only one mineral, that is made up of quartz and often includes impurities.
Septaria on a black metal base. A concretion of marly or argillaceous limestones containing angular cavities or cracks. These cracks (septaria) can be radiating or concentric and are often filled by the cementation of calcite and barite crystals.
Tabajaran mine on a Corten base. Agate, a variety of calchedony, has a typical zoned structure that is visible to the naked eye thanks to the differences in colour.
Rock crystal, also known as hyaline quartz, is the "ultimate" crystal: clear and transparent, able to break down white light into the colours of the rainbow.
Three cubical pyrite crystals from the famous mines in Spain. Pyrite is a mineral made up of iron disulfide, with a yellow-gold colour and a metallic shine.
A sedimentary formation that is common in desert areas. Its colours range from orange to ochre yellow and it is a cluster of gypsum crystals that is formed under very specific environmental and climatic conditions. This specimen is particularly large. [..]
Interlocking cubes, easily extracted from the Marna basin where they were formed 130 million years ago. The cubes in this extraordinary specimen are particularly large.
A tree branch that fell on the banks of the lake during the winter. Australia's many lakes are rich in sulphates, which create the perfect conditions for the cristallisation and formation of alites, gypsum and alunites.