Nekoite

Chemical formula: Ca₃Si₆O₁₅(H₂O)₅·₂H₂O

Nekoite is a rare calcium silicate, forming delicate, fibrous aggregates with a pearly or silky luster, resembling okenite in appearance.

## Characteristics Nekoite is a hydrated calcium silicate, most commonly found in the form of radial or spherical aggregates composed of fine, acicular or hair-like crystals. Its aggregates can be extremely delicate and visually very similar to okenite, with which it is closely related and often co-occurs. Individual "needles" are flexible, and the entire aggregate is soft and lightweight. Due to its delicate structure, it is a mineral valued mainly by collectors specializing in rare specimens. ## Physical Properties Nekoite crystals are very soft, with a Mohs hardness of just 1. They are characterized by a pearly luster on cleavage surfaces and a silky luster in fibrous aggregates. They are transparent to translucent. The mineral's density is low, approximately 2.24 g/cm³. ## Colors and Varieties Nekoite is usually colorless or white. No colored or commercial varieties are distinguished. ## History and Name The name "nekoite" comes from the Japanese word "neko," meaning "cat," and refers to its occurrence in the Neko mine in Okayama Prefecture, Japan, where it was first identified. The mineral was described and approved by the International Mineralogical Association (IMA) in 1959. The authors of the first description were Japanese mineralogists Takeo Ueda and Minoru Tateuchi.

Properties

Mohs hardness: 1
Color: White
Luster: Pearly
Streak: White
Density: 2.21
Cleavage: On {010}, distinct.
Fracture: Uneven
Transparency: Transparent,Translucent
Crystal system: Triclinic

Diagnostic features

## Identification Nekoite is recognized by its characteristic, radial aggregates of white, acicular crystals with a silky or pearly luster. Its extreme softness (Mohs hardness of 1) and very low density are key diagnostic features. It often occurs in cavities within basaltic rocks. ## Distinguishing from Similar Minerals Nekoite is visually almost identical to **okenite**. Distinguishing these two minerals without advanced analysis (e.g., XRD) is practically impossible. Nekoite forms triclinic crystals, while okenite crystallizes in the same system but differs in unit cell parameters and slightly in chemical formula. Both minerals often co-occur in the same localities, forming similar spherical aggregates. ## Crystal Forms Crystals are elongated, bladed, or acicular and very thin. They typically form radial, stellate, or spherulitic aggregates, as well as fibrous and felted masses.

Geological environment

## Genesis Nekoite is a secondary mineral, formed by low-temperature hydrothermal processes. It forms in vesicles and fractures of volcanic basic rocks, such as basalts and andesites. It results from the alteration of primary minerals under the influence of circulating solutions rich in calcium and silica. ## Mineral Associations This mineral most commonly co-occurs with okenite, apophyllite, calcite, quartz, and various minerals from the zeolite group, such as stilbite or heulandite. ## Localities Important nekoite localities worldwide include the Neko mine, Fuka, Okayama Prefecture, Japan (type locality); the Lake Superior region around Isle Royale in Michigan, USA; quarries near Brampton, England; Poona and Mumbai in Maharashtra, India; and Disko Island, Greenland.

Rarity

Rare

For collectors

## Quality Criteria The most prized nekoite specimens are those that form well-developed, spherical or radial aggregates of pure, white color and silky luster. The size and completeness of the spherulite, as well as its aesthetic placement on the rock matrix, often accompanied by contrasting minerals like apophyllite, are important. Due to its extreme delicacy, the intact condition of the specimen is a crucial factor. ## Popular Localities Classic and most sought-after specimens by collectors come from localities in Maharashtra, India (especially the Poona region), where large, impressive aggregates were found in basaltic cavities. Specimens from the type locality in Japan and historical localities in the USA (Michigan) are also valuable.

Care and storage

## Cleaning Nekoite specimens are extremely delicate and fragile. They should not be cleaned mechanically or chemically. The only permissible method is to very carefully remove loose contaminants using a stream of compressed air from a safe distance. ## What to Avoid Avoid contact with water, which can damage the delicate fibers. The mineral is very soft, so it must be protected from any touch, pressure, or vibrations. Also, avoid all chemicals, ultrasonics, and temperature changes. ## Storage Nekoite requires storage in a sealed, stable "micromount" container or in a display cabinet, away from dust, moisture, and vibrations. It is best displayed under glass or in an acrylic box to prevent accidental damage.