Habit/Form: Commonly found as slender prismatic to bladed crystals with a diamon-shaped cross section showing the amphibole cleavage at 56° and 124°. Also found as anhedral to strongly irregular grains, which in some cases may poikilitically enclose associated minerals.

2023年4月23日 · In PPL a thin section of Hornblende ranges from yellow -green to dark brown. Green varieties usually have X= light yellow green, Y=green or grey-green and Z=dark green. Brownish varieties have X=greenish-yelow/brown, Y=yellowish to reddish brown and Z=grey to …

Numerous common amphiboles can be represented within the Mg 7 Si 8 O 22 (OH) 2 (anthophyllite), Fe 7 Si 8 O 22 (OH) 2 (grunerite) and Ca 7 Si 8 O 22 (OH) 2 (hypothetical pure calcium amphibole) compositional field (Fig.1). This diagram is commonly referred to as the amphibole quadrilateral.

Photomicrographs of a thin section containing an amphibole crystal; under cross-polarized light on the left, and plane-polarized light on the right. Amphiboles crystallize into two crystal systems, monoclinic and orthorhombic. [4] In chemical composition and general characteristics they are similar to the pyroxenes. The chief differences from ...

Distinguishing the different amphiboles in thin section can be challenging, but there are some straightforward workflows. The YouTube video linked here gives an overview. In particular, low-Fe amphiboles (anthophyllite, Fe-poor gedrite, tremolite, cummingonite) are colorless in plane-polarized (PP) views.

Amphiboles in thin section Amphiboles at the microscale can be easily identified based on the same features that allow their recognition in the field, in particular the presence of perfect prismatic cleavage planes that intersect at nearly 60 – 120°.

Thin section: Plane light: Moderate to moderately high positive relief. Colorless to medium blue in thin section for Glaucophane to dark blue for Riebeckite. Both are distinctly pleochroic.

One way to distinguish amphibole from pyroxene in thin section is by its roughly 60° (or 120°) cleavage in basal sections (Figure 46). Most often the cleavage is parallel and amphiboles have inclined extinction.

In thin section it is distinguished from wollastonite and diopside by its amphibole cleavage. In thin section it is clear with no pleochroism, which distinguishes it from other amphiboles. It shows high relief, inclined extinction, and is optically negative with a 2V of about 85 o.

2021年5月3日 · All minerals in the amphibole group are characterized by perfect cleavage in two directions and a splintery fracture. Colours are typically dark green, brown or black.