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It exhibits a hardness of 2 on the Mohs hardness scale. [3] Scotlandite occurs as chisel-shaped or bladed crystals elongated along the c-axis, with a tendency to form radiating clusters. Its crystals are characterized by the {100}, {010}, {011}, {021}, {031}, and {032}. faces. Scotlandite shows perfect cleavage along the {100} plane and a less ...
Recognizing the habit can aid in mineral identification and description, as the crystal habit is an external representation of the internal ordered atomic arrangement. [1] Most natural crystals, however, do not display ideal habits and are commonly malformed. Hence, it is also important to describe the quality of the shape of a mineral specimen:
Amethyst crystals – a purple quartz Apophyllite crystals sitting right beside a cluster of peachy bowtie stilbite Aquamarine variety of beryl with tourmaline on orthoclase Arsenopyrite from Hidalgo del Parral, Chihuahua, Mexico Aurichalcite needles spraying out within a protected pocket lined by bladed calcite crystals Austinite from the Ojuela Mine, Mapimí, Durango, Mexico Ametrine ...
Hornblende has a hardness of 5–6, a specific gravity of 3.0 to 3.6, and is typically an opaque green, dark green, brown, or black color. It tends to form slender prismatic to bladed crystals, diamond-shaped in cross section, or is present as irregular grains or fibrous masses.
Riebeckite is a sodium-rich member of the amphibole group of silicate minerals, chemical formula Na 2 (Fe 2+ 3 Fe 3+ 2)Si 8 O 22 (OH) 2. It forms a solid solution series with magnesioriebeckite. It crystallizes in the monoclinic system, usually as long prismatic crystals showing a diamond-shaped cross section, but also in fibrous, bladed ...
Well developed crystals of epidote, Ca 2 Al 2 (Fe 3+;Al)(SiO 4)(Si 2 O 7)O(OH), crystallizing in the monoclinic system, are of frequent occurrence: they are commonly prismatic in habit, the direction of elongation being perpendicular to the single plane of symmetry.
Actinolite is an intermediate member in a solid-solution series between magnesium-rich tremolite, Ca 2 (Mg 5.0-4.5 Fe 2+ 0.0-0.5)Si 8 O 22 (OH) 2, and iron-rich ferro-actinolite, ☐Ca 2 (Mg 2.5-0.0 Fe 2+ 2.5-5.0)Si 8 O 22 (OH) 2. Mg and Fe ions can be freely exchanged in the crystal structure. Like tremolite, asbestiform actinolite is ...
The color is the same as its dimorph, pentagonite, but the latter is generally much more spikey with bladed crystals. Finally, the associated minerals are useful for identification, as cavansite is frequently found sitting atop a matrix of zeolites or apophyllites.