2026 Undergraduate Research Showcase

Taking a “Peak” at Apatite: Towards a Quantitative Calibration of Hydroxyl Content in Apatite by Raman Spectroscopy

Document Type

Student Presentation

Presentation Date

4-24-2026

Faculty Sponsor

Dr. Matthew Kohn

Abstract

The hydroxyl (OH) content of apatite [Ca5(PO4)3(F, OH, Cl)] is of potential value for mineral thermobarometry and for assessing volatile contents of magmas, but is notoriously difficult to measure. Here, we explore the potential to use Raman spectroscopy to quantify OH contents in situ at the micron scale in apatite. For this project 6 mm polished apatite beads were analyzed on a Horiba LabRAM Raman microscope using a 442 nm (blue) laser at 100% power. Two results emerge from our data; first, orientation affects the intensity of the OH band independent of the OH content. Consequently, neither the OH peak height nor the peak height ratio of OH to v1 PO4 can directly infer OH content. Rather, OH peak intensity and OH/v1 PO4 are highest when the beam is parallel to the c-axis and are lowest when the beam is perpendicular to the c-axis. Second, crystal orientation affects the intensity ratio of the v3/ v1 PO4 peaks and splitting of the v2 (c. 450 cm-1), v4 (c. 600 cm-1), and v3 (c. 1050 cm-1) PO4 regions, less splitting of v2, v3, and v4 occurs when the beam is parallel to the c-axis, and more splitting occurs when the beam is perpendicular to the c-axis. Using these characteristics, we are working towards a calibration for OH content that corrects for crystal orientation.

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