What is Jennite?
Jennite is a hydrated calcium silicate with delicate fibrous aggregates, best known from altered limestone and cement-related mineralogical studies.
Mineralogy and crystal structure
Reference formula: Ca9Si6O18(OH)6·8H2O. Jennite has a triclinic structure containing wollastonite-type silicate chains and calcium-oxygen layers with molecular water. It is a hydrated mineral and can be sensitive to heat and dehydration. Jennite is classified with silicates and has a triclinic crystal system. Typical hardness is 3–3.5 on the Mohs scale and specific gravity is approximately 2.3–2.4.
Colour, lustre and habit
Typical colours include white, colourless, pale yellow. The usual fibrous, radiating, massive habit and vitreous, silky, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Jennite forms in or is associated with contact-metamorphic limestones, calcium-silicate assemblages and altered cementitious systems. Important documented localities include the United States, Italy, Germany and other calcium-silicate localities.
Subtle beauty for a micro-mineral collection
Jennite is not a flashy showroom stone; its appeal is the soft, fibrous texture and the way it documents the chemistry of calcium-rich environments. A well-labelled micro-mount can turn an understated white mineral into a sophisticated study specimen.
A mineral of fine structure
The radiating habit is sometimes described through modern metaphors of growth and connection. These are aesthetic interpretations only; Jennite's real distinction is the unusual hydrated calcium-silicate architecture shown in its structure model.
Collecting and care
Keep dry and away from heat; protect silky fibres from abrasion and do not powder unknown calcium-silicate material.
