Mineralpedia Details for Astrophyllite

Formula

K₂NaFe²⁺₇Ti₂(Si₄O₁₂)₂O₂(OH)₄F 

Crystal System

Triclinic 

Crystal Habit

Bladed, Stellate, Crystalline - Fine 

Cleavage

Perfect, None, None 

Luster

Adamantine - Pearly 

Color

brown, brownish red, bronze yellow, gold yellow 

Streak

yellowish brown 

Class

Triclinic - Pedial 

Fracture

Brittle 

Hardness

3-3.5 

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Deep reddish brown long bladed crystals to 3.5cm.

Astrophyllite is NOT a mica but is an inosilicate, which can resemble mica plates in hand specimen, as is the case and with most of the Astrophyllite. Astrophyllite has a perfect cleavage, can be split like a mica in thin sheets, but is very brittle (Ency. of Minerals). The color is much like a mica also being a bronze to orange yellow. Usually found in pegmatites of nepheline syenites, alkaline granites of MSH and Magnet Cove (typical for titanium minerals). Finest crystals come from Khibiny massif (Bernard & Jaroslav).

A nice specimen with long bronze plates of Astrophyllite to 2.5cm and a large crystal of Aenigmatite to 4.5cm.

Astrophyllite is NOT a mica but is an inosilicate, which can resemble mica plates in hand specimen, as is the case. Astrophyllite has a perfect cleavage, can be split like a mica in thin sheets, but is very brittle (Ency. of Minerals). The color is much like a mica also being a bronze to orange yellow. Usually found in pegmatites of nepheline syenites, alkaline granites of MSH and Magnet Cove (typical for titanium minerals). Finest crystals come from Khibiny massif (Bernard & Jaroslav).

This is a smaller specimen but with beautiful elongated bronze crystals to 1cm.

Long excellent blades to 4cm of golden brown Astrophyllite. This is an old University of Chicago piece from Paul Moore. See prov. tab.

Long bladed golden crystals to over 2cm.

Astrophyllite is an inosilicate with a {010} perfect cleavage. This specimen shows beautiful groups of radial bronze, bladed crystals 6mm resembling a mica in Albite matrix. However, it is not phyllosilicate and thus not a mica either. It typically occurs in pegmatites, nepheline syenites and alkaline granites such as Mont Saint-Hilaire, 

At first glance this looks like a biotite mica. It is actually not even micaceous even though it looks micaceous. The crystals are brown, shiny, and platy, which only looks like mica but is placed in this Special Edition to show the similarity of the two minerals.