BH250-37
Title
BH250-37
Subject
C-axis Apatite
Major Mineral: Apatite
Mineralogy Comments: Apatite grain cut perpendicular to the c-axis.
Optics: A centered optic axis figure shows a black cross (isogyres) with a central point—the melatope—marking the emergence of the optic axis. Due to apatite’s low birefringence, isochromes are typically absent or very faint around the melatope.
When viewed with a sensitive tint plate (mica), addition (yellow) appears in quadrants I and III, and subtraction (blue) in quadrants II and IV, consistent with a uniaxial negative optic sign.
Many thin sections contain apatite grains, often small, making it challenging to obtain clear interference figures. However, when a grain is cut parallel to the c-axis, the length fast / length slow method can be applied to determine the optic sign and axis orientation. An example of this is found in sample BH250-173b.
Major Mineral: Apatite
Mineralogy Comments: Apatite grain cut perpendicular to the c-axis.
Optics: A centered optic axis figure shows a black cross (isogyres) with a central point—the melatope—marking the emergence of the optic axis. Due to apatite’s low birefringence, isochromes are typically absent or very faint around the melatope.
When viewed with a sensitive tint plate (mica), addition (yellow) appears in quadrants I and III, and subtraction (blue) in quadrants II and IV, consistent with a uniaxial negative optic sign.
Many thin sections contain apatite grains, often small, making it challenging to obtain clear interference figures. However, when a grain is cut parallel to the c-axis, the length fast / length slow method can be applied to determine the optic sign and axis orientation. An example of this is found in sample BH250-173b.
Description
Major Mineral: apatite
Mineralogy Comments: apatite cut perpendicular to C-axis
Mineralogy Comments: apatite cut perpendicular to C-axis
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample 37. Housed at Carleton College in Minnesota.
Type
Thin section
Relation
View on ArcGIS Online here
Collection
Citation
Bereket Haileab, “BH250-37,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/41.