Smith College - Geology 222b - Petrology

Petrographic Data File

Crystal System

Crystal Habit

Short, stubby, prismatic crystals with square, rectangular, or eight sided cross section
Granular, lamellar, or columnar masses
Anhedral grains

Fair to good cleavage on (110)
Partings on (100) and (001)
Imperfect cleavage intersecting at 87º and 93º


White to light green
No pleochroism
Colorless to pale green in thin section

Optic Sign
Biaxial (+)

Optic Orientation
X^a = -20º to -33º, Y = b, Z^c = +35º to +48º
Refractive Indices
alpha =
beta =
gamma =
delta =

Max Birefringence


Elongation parallel to c axis
inclined in (010) sections .
r > v
- weak to strong
Distinguishing Features
light green color, cleavage

Commonly found in metamorphosed carbonate rocks like skarns and marbles.

Found with: tremolite, actinolite, grossular garnet, epidote, wollastonite, forsterite, calcite and dolomite

Ruth Indrick ('08), Brittany Holt ('15), June Cadenhead ('16)
Nesse, 2000; Blackburn and Dennen, 1988; Klein and Hurlbut, 1977

Diopside is the pale green mineral in the center that has high birefringence and appears second order pink when viewed under crossed polars. The reddish isotropic mineral, found at the top right corner and the top left, is garnet. The clear mineral on the left hand side that appears yellow under crossed polars is wollastonite.

Photomicrograph of diopside in plane polarized light. Diopside is the pale green mineral at the center of the photo that turns second order yellow under crossed polars. The reddish mineral to the left is garnet, and wollastinite appears at the lower right of the screen.

Diopside tends to display fairly prominent cleavage at about 90°

Photomicrograph of diopside in plane polarized light. Diopside is the pale green mineral at the top of the photo; it is surrounded by reddish garnets on the lower side, and a grain of wollastinite is visible on the lower left. This diopside displays second order pink under crossed polars.

Notice that diopside, the mineral centered in the frame has distinct 90° cleavage. In Plain Polarized Light, diopside is a pale green mineral and under cross polarized light, this diopside is second order yellow. The mineral found at the top left corner of the frame is also diopside but appears second order green/blue because it is showing a different plane.

Diopside, the mineral centered in the frame, is pale green in plain polarized light and first order yellow in crossed polar light. It has clear 90° cleavage and is typically found with forsterite. The location that this sample was taken is along Route 2 towards Boston.

These photographs show a first order yellow Diopside mineral through the Bertrand Lens. The first view shows the 2V (55 ±10) and the second view illustrates the Optic Sign (+).

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