Characteristics of Fluorescent Inclusions in Quartz Crystals Hosted by Organic-Rich Black Limestone in Sakawa Town, Kochi Prefecture, Southern Shikoku, Japan

Abstract

The Torinosu Limestone in Sakawa Town, Kochi Prefecture, Japan, is rich in organic matter and has long been recognized as a black limestone with a high concentration of organic material. Quartz containing petroleum-like substances occurs in veins within this black limestone. The quartz hosting these petroleum-like fluid inclusions typically exhibits a bipyramidal to tabular habit. Under ultraviolet light, the fluid inclusions display intense fluorescence. The polycyclic aromatic hydrocarbon (PAH) fraction extracted from the fluorescent quartz contains significant amounts of methylnaphthalene and methylphenanthrene, which are responsible for the observed fluorescence. In addition to these compounds, unsubstituted pyrene, chrysene, and perylene were detected in the black limestone. Methylnaphthalene, methylphenanthrene, and squalene—the primary fluorescent components—were likely derived from the organic-rich black limestone during the formation of the quartz veins and subsequently incorporated into the quartz.