Guarinoite

Chemical formula: Zn₂+₆S₆+O₄(OH)₁₀·₅H₂O

Guaraninoite is a very rare, hydrated zinc sulfate, forming microscopic, colorless or white tabular crystals.

## Characteristics Guaraninoite is a mineral belonging to the sulfate group. It occurs as very small, tabular or platy crystals, rarely exceeding 0.2 mm in length. The crystals are typically colorless to white and transparent. Due to their microscopic size, its visual features are difficult to observe without specialized equipment. ## Physical Properties Guaraninoite crystals exhibit a vitreous luster. Hardness and density have not been precisely measured due to the small size of the samples, but the Mohs hardness is estimated to be around 2. It is a very soft mineral. ## History and Name Guaraninoite was discovered in the "Vignola" mine, near the town of Sestri Levante in Liguria, Italy. It was described and approved as a new mineral by the IMA in 1991. The name honors the Italian mineral collector, Antonio Guarino (born 1943), who found the first samples of this mineral.

Properties

Mohs hardness: 2
Luster: Vitreous
Streak: White
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Transparent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of guaraninoite is only possible using advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD), combined with chemical analysis (EDS). Visual identification in the field or even in a collection is impossible due to its microscopic size and lack of characteristic macroscopic features. ## Distinguishing from similar minerals Guaraninoite can be confused with other secondary zinc sulfates, such as namuwite, lannonite, or serpierite, which often coexist in similar environments. Differentiation requires specialized laboratory tests. ## Crystal forms It forms microscopic, hexagonal crystals with a tabular or platy habit. Crystals often occur as rosette-like or radial aggregates on the surface of the host rock.

Geological environment

## Genesis Guaraninoite is a secondary mineral, forming in the oxidation (weathering) zones of zinc-rich sulfide deposits. It forms as a result of sulfate-rich waters acting on zinc minerals, such as sphalerite. It forms under low-temperature conditions, often in voids and fractures of rocks. ## Mineral associations It most commonly coexists with other secondary zinc and copper minerals. Typical associated minerals include sphalerite (as a primary mineral), gypsum, serpierite, namuwite, schulenbergite, lannonite, and ktenasite. ## Localities The most important and type locality (località tipo) is the "Vignola" mine in Liguria, Italy. It has also been identified in several other locations worldwide, including the "Esperanza" mine in Lavrion, Greece, and the "Friedrichssegen" and "Grube 7" mines in Rhineland-Palatinate, Germany. All these localities are known for the occurrence of rare secondary minerals.

Rarity

Very rare

For collectors

## Quality criteria For a mineral as rare as guaraninoite, the main criterion of value is the confirmed presence of the mineral on the sample itself. The most highly prized specimens are those where the crystals, despite their microscopic size, form well-defined aggregates (e.g., rosettes) and are richly dispersed on a small rock matrix. Color contrast with the substrate also enhances the visual appeal of the specimen under a microscope.

Care and storage

## Cleaning Due to its extreme rarity and fragility, guaraninoite specimens are practically not subject to cleaning. Any attempts at mechanical or chemical cleaning risk irreversible destruction of the microscopic crystals. If it is necessary to remove loose dust, a gentle stream of compressed air can be used from a distance. ## What to avoid Avoid contact with water, chemicals, ultrasound, and any vibrations or impacts. The mineral is very soft and brittle. Store away from heat sources and humidity. ## Storage Guaraninoite specimens should only be stored in specialized, sealed "micromount" boxes, protecting them from dust, moisture, and mechanical damage. Display is only possible under a microscope.

Sources

IMA Mineral List (CNMNC)