Document Type

Thesis

Date of Degree Completion

Spring 2007

Degree Name

Bachelor of Science

Department

Geological Sciences

Committee Chair

Dr. Paul W. O. Hoskin, Department of Geological Sciences

Second Committee Member

Dr. Andrew A. Piacsek, Science Honors Research Program Director

Abstract

Agate is a silica-rich rock that preserves a record of ancient hydrology and water/rock interaction. However, there is little consensus on how agate forms. Two end­member formation models exist for agate hosted by basalt and are tested here by trace element investigation of agate samples from Brazil, Germany, and Washington, USA. Trace element abundances were analyzed by laser ablation ICP-MS and the data indicate crystallization in a closed system, at least on the scale of analysis in thin-section. Field data, X-ray diffraction data, and stable isotope analyses indicate that ~50 Ma agate from central Washington formed from heated meteoric water. These results conform to studies of basalt-hosted agate in other worldwide occurrences and lead to the conclusion that these agate occurrences form in geologically cool (50-60 °C), meteoric water dominated systems where crystallizing fluids precipitate quartz into striking banded textures in a self-organizing closed-system.

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