Barkevikite
Barkevikite is an obsolete name (discredited in 1978) for an occurance of Ferro-edenite from pegmatitie formations in the eastern part of the Langesudsfjord area of Norway. Ferro-edenite is a fairly rare member of the Calcic Clino-Amphibole Subgroup of the Amphibole Group of minerals that includes Actinolite, Ferro-edenite, Kaersutite, Pargasite, Richterite and Tremolite. The Amphibole Group is an extensive and complex group of minerals currently divided into several sub-groups. Ferro-edenite is almost identical to the more common Amphibole mineral Edenite but contains more iron than magnesium, thus the name Ferro-edenite (ferro is Latin for iron). Ferro-edenite is generally darker and more dense.
Ferro-edenite is available from the Baie-des-Moutons complex, La Tabatiμere, Quebec, Canada; the Tibchi ring complex, Nigeria; Skudesundskjær (Skutesundskjær), Barkevik (Barkevika), Langesundsfjorden, Larvik, Vestfold, Norway; Hendersons Quarry, Mt. Ngongotaha, Rotorua, Bay of Plenty, North Island, New Zealand. Ferro-edenite undoubtedly occurs at other localities but qualifying analyses appear lacking.
| Chemical Formula: | NaCa2(Fe2+)5(Si7Al)O22(OH)2 |
| Sodium Calcium Iron Aluminum Silicate Hydroxide | |
| Molecular Weight: | 991.96 gm |
| Composition: | Sodium | 2.32 % | Na | 3.12 % | Na2O |
| Calcium | 8.08 % | Ca | 11.31 % | CaO | |
| Aluminum | 2.72 % | Al | 5.14 % | Al2O3 | |
| Iron | 28.15 % | Fe | 36.21 % | FeO | |
| Silicon | 19.82 % | Si | 42.40 % | SiO2 | |
| Hydrogen | 0.20 % | H | 1.82 % | H2O | |
| Oxygen | 38.71 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Commonly as well-formed prismatic crystals; fibrous; as reaction rims on pyroxenes. |
| Twinning: | Simple or multiple twinning || {100} |
| Cleavage: | Distinct/Good on {110} |
| Fracture: | Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 5.0 – 6.0 |
| Density: | 4.62 – 4.73 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Black, dark Green |
| Transparency: | Semi-Transparent to Opaque |
| Luster: | Vitreous |
| Refractive Index: | 1.650 – 1.730 Biaxial ( – ) |
| Birefringence: | 0.0200 |
| Dispersion: | Weak to Strong; r > v |
| Pleochroism: |
Distinct; X = yellow; Y = green; Z = dark green |
