TERRIUM — A mineralogy cabinet

Antofilita Bola o nódulo de Heřmanov

Antofilita is a mineral with formula (Mg,Fe²⁺)₇Si₈O₂₂(OH)₂ + KMg₃(AlSi₃O₁₀)(OH)₂, in the Anfíboles group. This specimen comes from Heřmanov, Žďár nad Sázavou, Vysočina, Región de Vysočina, República Checa.

Antofilita Bola o nódulo de Heřmanov from Heřmanov, Žďár nad Sázavou, Vysočina, Región de Vysočina, República Checa — Terrium

Description

Spheroidal nodule of near-perfect symmetry with canonical "onion" structure: a dark, lustrous phlogopite (mica) core surrounded by a radial rim of beige-green anthophyllite fibres with silky lustre. Zonation is intact and clearly shows the mineralogical transition from centre to periphery without recent fractures.

About Antofilita

The famous "Heřmanov Balls" ("Heřmanovské koule") formed by a contact reaction: a silica-rich pegmatite vein cut a silica-poor rock at the contact between granulites and ultramafic rocks. To balance that chemical contrast, a reaction zone (the ball) developed in which core phlogopite was progressively transformed into anthophyllite towards the rim.

About the locality

Heřmanov is a small village in the Bohemian Highlands (Vysočina) that put its name on the world map thanks to these unique nodules. Declared a "Natural Monument" in 1978. As a protected site, collecting is restricted, so quality, complete specimens usually come from old collections.

Technical data

Catalogue No.
0276
Composition
(Mg,Fe²⁺)₇Si₈O₂₂(OH)₂ + KMg₃(AlSi₃O₁₀)(OH)₂
Name
Antofilita
Variety
Bola o nódulo de Heřmanov
Group
Anfíboles
Category
Meritum Persé
Matrix
Flogopita
Associations
Clorito
Mine
Heřmanov
District / Municipality
Žďár nad Sázavou
Province
Vysočina
Region
Región de Vysočina
Country
República Checa
Size (cm)
5.5 x 5.5 x 2.7
Weight
103.2 g
Ex-collection
Sergio Petretich
Etymology
From the Greek "anthos" (flower) and "phyllon" (leaf), for the fibrous and platy aspect of its crystals.
Quality
Muy buena
Value trend
Estable

Related specimens

← Back to Terrium catalogue