Probably one of the most common incorrectly labeled crystals is Arfvedsonite. More times than not, when you look to purchase Astrophyllite you are most likely buying Arfvedsonite. I too have fallen victim to this, so believe me when I say that you are not alone! Seeing these crystals side by side and knowing what coloring to look for will make a huge difference in knowing if you’re looking at Arfvedsonite or Astrophyllite.
Astrophyllite: Golden yellowish-brown.
Arfvedsonite: Dark bluish-gray.
Color and Mineral Content:
Astrophyllite: Astrophyllite is always a bronze, reddish brown color. You will never find it as blue, silver, or yellow like you will with Arfvedsonite. It grows in a Nepheline Syenite matrix, which is typically an off white to gray in color. Astrophyllite can grow with other stones such as Eudialyte and Aegirine. Astrophyllite has the chemical composition of K2NaFe2+7Ti2Si8O26(OH)4F (Potassium Sodium Iron Manganese Titanium Silicate Hydroxide). (Click here to read more about Astrophyllite.)
Arfvedsonite: Arfvedsonite color is bluish-black to black. It has a strong pleochroism (change of color under plane-polarized light) in the colors of blue-greens, yellow-browns, and gray-violets. The dark reddish color that often grows with Arfvedsonite is Eudialyte (not Garnet). Arfvedsonite can also grow with Aegirine as well as many other minerals. Arfvedsonite has the chemical composition of [Na][Na2][Fe2+4Fe3+]Si8O22(OH)2 (Sodium Iron Magnesium Silicate Hydroxide). It is a basic sodium iron silicate, sometimes with some potassium, magnesium, and fluorine. There are several variations of Arfvedsonite with different elemental substitutions. (minerals.net) (Click here to read more about Arfvedsonite.)
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