Morenosite
Chemical formula: Ni<sup>2+</sup>S<sup>6+</sup>O<sub>4</sub>·7H<sub>2</sub>O
Morenosite is a hydrated nickel sulfate, forming characteristic apple-green efflorescences and crusts that are unstable in dry air.
Description
## Characteristics Morenosite is a secondary mineral from the sulfate group, chemically a hydrated nickel sulfate. It most commonly occurs as efflorescences, coatings, and crusts with a microcrystalline or fibrous structure. Less frequently, it forms small, acicular or prismatic crystals, as well as botryoidal forms resembling small stalactites. Its most characteristic feature is an intense, apple-green color, which can transition to lighter, greenish-white or almost white shades. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 2 to 2.5, meaning it can be scratched with a fingernail. It exhibits a vitreous luster and is transparent to translucent. Its density is low, approximately 1.95 g/cm³. It is brittle and readily dissolves in water. A key property of morenosite is its instability in dry air – it then loses its crystallization water and transforms into nickel sulfate hexahydrate (retgersite), often taking on a yellowish hue and becoming powdery. ## Colors and Varieties The dominant and almost sole color of morenosite is a vivid, apple-green, typical of many hydrated nickel compounds. The intensity of the color depends on the degree of hydration and chemical purity. No distinct color or commercial varieties are recognized. ## History and Name The mineral's name, given in 1851 by the Spanish chemist and pharmacist, José Luis Casares, commemorates Antonio Moreno Ruiz (1796-1852), a Spanish professor of chemistry and pharmacy. The type locality, from which the first described material originated, is the vicinity of Cape Ortegal in Galicia, Spain. ## Uses Morenosite has no industrial significance. It is of interest only to mineral collectors and scientists studying the weathering processes of sulfide deposits.
Diagnostic features
## Identification Key diagnostic features of morenosite are its apple-green color, very low hardness (2-2.5), and its occurrence as efflorescences and coatings. The most important test is to observe its behavior: in dry air, it quickly dulls and disintegrates, and upon contact with water, it dissolves. Its occurrence in the oxidation zones of nickel deposits is a strong indicator. ## Distinguishing from Similar Minerals Morenosite is sometimes confused with other secondary nickel minerals and sulfates: - **Annabergite (nickel bloom)**: Has a very similar color but is an arsenate, not a sulfate. It usually forms more well-developed acicular crystals and is stable under atmospheric conditions. - **Retgersite**: Is a dehydration product of morenosite. It has less water in its structure (six H₂O molecules), often a yellowish tint, and crystallizes in the tetragonal system. - **Melanterite**: A hydrated iron sulfate that can have a greenish color, but usually with a bluish tint. It is also water-soluble but is associated with pyrite deposits, not nickel minerals. ## Crystal Forms Well-formed crystals are rare and usually microscopic, appearing as acicular or short prismatic forms. It is most commonly found as fibrous aggregates, earthy, powdery coatings, crusts, and small stalactites in rock cavities and on the walls of old mine workings.
Geological environment
## Genesis Morenosite is a typical secondary mineral. It forms as a result of the weathering and oxidation of primary nickel sulfides, such as millerite, niccolite, or gersdorffite. This process occurs in the oxidation zones (gossan) of hydrothermal ore deposits. It currently forms as a product of evaporation of nickel-rich mine waters, growing on the walls, ceilings, and supports of old adits and mine shafts. ## Mineral Associations This mineral occurs in association with primary nickel sulfides (millerite, niccolite, gersdorffite) and other secondary nickel minerals and sulfates, such as annabergite, retgersite, and epsomite. ## Localities Important localities worldwide include: the historical type locality in Spain (Cape Ortegal, Galicia); numerous sites in Germany (Saxony, North Rhine-Westphalia); Italy (Piedmont); Czech Republic (Jáchymov); Austria (Styria). It is also known from some deposits in the USA (Missouri, Nevada) and Canada (Ontario).
Rarity
Not very common
Collector aspects
## Quality Criteria The most highly valued morenosite specimens are those with visible, even if small, crystals. Due to their rarity, even microcrystalline druses are sought after. The intensity and purity of the apple-green color and the abundance of the mineral on the host rock (matrix) are important. Specimens preserved in a stable form, without signs of dehydration, are significantly more valuable. Association with well-formed crystals of primary minerals, e.g., millerite, is a great asset. ## Popular Localities Among collectors, specimens from classic European localities, especially Germany, which have provided many well-preserved samples, are highly regarded. Material from deposits in the Siegen region (Germany) and the Gesso Valley in Italy is often found in collections.
Care and storage
## Cleaning Morenosite is extremely sensitive. It must absolutely not be cleaned with water or any liquids, as it dissolves in them. Only very gentle, mechanical dust removal with a soft brush or a stream of compressed air from a distance is permissible. ## What to Avoid Contact with water and other liquids must be strictly avoided. The greatest threat is dry air, which causes its dehydration (loss of water) and disintegration into powder. It should also be protected from elevated temperatures and direct sunlight, which accelerate this process. ## Storage Morenosite specimens require storage under special conditions. The best solution is a sealed, airtight container (e.g., a "membrane box" or a box with a gasket) in which stable, elevated humidity is maintained. Some collectors place a small piece of damp material (without direct contact with the specimen) in the container to prevent drying out. Store in a dark and cool place.