Aegirine
NaFe3+Si2O6 [CNMNC approved formula]
Named after the Teutonic god of the sea. Acmite is from the Greek "point" in allusion to the pointed crystals.
| IMA status : | Approved Species 1835 () |
| CLASSIFICATION | |
| Dana (8th edition) : |
65.01.03c.02 |
| (65) Inosilicate Single-Width Unbranched Chains, W=1 | |
| (65.01) with chains P=2 | |
| (65.01.03c) C2/c clinopyroxenes (Na clinopyroxenes) | |
| Nickel-Strunz (10th edition) : |
09.DA.25 |
| (09) Silicates | |
| (09.D) Inosilicates* Structural terminology per Liebau (1985) | |
| (09.DA) with 2-periodic single chains, Si2O6; pyroxene family | |
| Crystal system: | Monoclinic System |
| Point group (H-M): | 2/m — prismatic |
| Space group: | C2/c |
| Unit cell: | a = 9.66 Å, b = 8.80 Å, c = 5.29 Å, b = 107.4° |
| Crystal Habit: | Crystals long prismatic, vertically striated or furrowed; tufts or acicular to capillary. |
| Twinning: | Common on {100}, simple or lamellar |
| Color: | Dark green to greenish black |
| Diaphaneity: | Translucent to opaque |
| Luster: | Vitreous to resinous |
| Hardness (Mohs): | 6 |
| Measured Density: | 3.50 to 3.60 g/cm3 |
| Cleavage: | 2; {110} good; {100} parting |
| Tenacity: | Brittle |
| Fracture: | Uneven |
| Streak: | Pale yellowish gray |
| Geologic Setting: | Common in alkalic igneous rocks, carbonatites, and pegmatites. From regionally metamorphosed schists, gneisses, and iron formations; in blueschist facies rocks, and from sodium metasomatism in granulites. An authigenic mineral in some shales and marls. |
| Mineral Association: | Potassic feldspar, nepheline, riebeckite, arfvedsonite, aenigmatite, astrophyllite, catapleiite, eudialyte, serandite, apophyllite |
| Synonyms/varieties: | Acmite, schefferite (Mn, Fe-rich var.) |
| Other Properties: | Gemstone Unlikely Available. |
Origin: 3M quarry, Little Rock, Pulaski Co., Arkansas, U.S.A.Sample size: Microscopic image
Photo and Owner: Lou Perloff
Origin: Magnet Cove, Arkansas, U.S.A.Sample size: 3 x 4 cm
Photo: Dan Weinrich
(zoom-in of above)