Mineralogy

Heřmanov sphere

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This unique rock consist of mushroomed phlogopite sphere in the middle, concentric antofyllite crystals around and another layer of phlogopite crystals. Sometimes the zone of chlorite with montmorillonite is developed between both minerals.

Phlogopite

Structural info:

phlogopite

Name origin:
From the Greek flogopos -“resembling fire.”

Phlogopite is a phyllosilicate mineral, member of mica group. It forms pseudohexagonal prismatic crystals, which are usually conic and sometimes also twinned. This mineral could also have foliated and flaky habitus. It is usually colourless,greenish, yellow or reddish-brown. Phlogopite has Pearly or  slightly metallic on cleavage surfaces. Its cleavage is perfect basal with no fracture. Phlogopite micas are found primarily in igneous rocks, although it is also common in contact metamorphic aureoles of intrusive igneous rocks with magnesian country rocks.

Anthophyllite

Structural info:

anthophyllite

Name origin:

“anthophyllum” from the Latin meaning “clove” (itself derived from the Greek άνθος for “flower” and φύλλον for “leaf” ), in allusion to its common clove-brown colour.

Description:

Anthophyllite is a member of  amphibole group. Anthophyllite is polymorphic with cummingtonite. It rarely forms as distinct crystals. Common are lamellar or fibrous, these are classed as asbestos. It has white, wreenish gray, wreen, clove brown or Brownish green colour and grey streak. Its cleavage is perfect on {210}, imperfect on {010}, {100} and fracture is conchoidal. Anthophylite is the product of metamorphism of magnesium-rich rocks, especially ultrabasic igneous rocks and shales. It is also formed as a retrograde product rimming relict orthopyroxenes and olivine, and as an accessory mineral in cordierite-bearing gneisses and schists. Anthophyllite also occurs as a retrograde metamorphic mineral derived from ultramafic rocks along with serpentinite.

This specimen was found in locality Velké Medziričí near the town Hermanov in Czech Republic. Spheres of this compositions are world uniquate! They are created in areas where pegmatite veins penetrate into the serpentine body. This locality is also known for its flora and it is sad this locality is being devastated by reckless collectors.