16 Geologic Maps, Geophysical Maps, Digital Geologic Maps, and Derivatives from Geologic and Geophysical Maps (Posters)

Thursday, 24 March 2011
1:30 PM - 5:30 PM
Exhibit Hall

APPLYING GEOCHEMICAL ANALYSIS OF MICA GRAINS TO FORENSIC INVESTIGATIONS: NORTH CAROLINA V. JORDAN PETERSON, WAKE COUNTY, NC

Paper number: 16-19
Program: Theme Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

Elemental compositions of individual white mica grains were examined to determine the possibility of a physical link between a suspect and the crime scene in the first degree murder trial, North Carolina v. Jordan Peterson. Mica collected from clothing evidence were analyzed for major elemental compositions and compared to elemental compositions of mica grains from the crime scene using a JEOL JXA 8530F Hyperprobe at Fayetteville State University in Fayetteville, North Carolina. In diagrams of Na2O vs. K2O and Al2O3 vs. K2O, two populations of mica and significant overlap of compositional fields were evident for the crime scene micas and the micas from the clothing evidence. In diagrams of SiO2 vs. MgO and FeO vs. MgO, micas from the crime scene and micas from the evidence show significant overlap in compositional fields and exhibit similar geochemical trends. The overlap in compositional fields and two populations of mica for the crime scene and evidence samples suggest they are consistent with each other.

The compositional data from the crime scene and evidence were also compared to compositions of white mica from “index samples” collected from three locations in the greater Raleigh area (the Falls Lake area, the Triangle Quarry and the Knightdale Quarry). Detailed geologic maps, partially funded by the STATEMAP program, allowed for effective selection of index sample locations. The compositional data suggest micas from the evidence and crime scene have different chemical compositions than the index sample micas.

Presentation of these data at the trial set a legal precedent in Wake County, North Carolina and played an important role in the jury’s decision, suggesting that geochemical techniques can be useful in forensic investigations. Research is ongoing to develop a regional database of mica compositions.