[M-IS23] 地質学のいま

[MIS23-P09] 水酸化ナトリウム水溶液を用いた放散虫化石処理法

*尾上 哲治¹、堀 早紀子¹、冨松 由希²、リゴ マニュエル³ (1.九州大学 、2.福岡大学、3.パドバ大学)

キーワード：チャート、放散虫、水酸化ナトリウム

Radiolarians have been studied throughout the Phanerozoic to determine geological ages and have contributed greatly to our understanding of Earth's history. Hydrofluoric acid (HF) has been used to extract radiolarian fossils from siliceous deposits (radiolarian chert), but this acid is currently strictly regulated due to environmental and human health concerns. Here we report the successful extraction of radiolarians from chert using a low concentration of sodium hydroxide (1 mol/L NaOH) as an alternative chemical to HF. The degree of dissolution of chert in NaOH solution is strongly temperature dependent, being less at 60 or 80°C. However, when heated to 100°C, we show that even a 1 mol/L NaOH solution is sufficient to dissolve the chert. Furthermore, this method has allowed us to obtain well preserved radiolarian fossils compared to the conventional HF method. The 1 mol/L NaOH solution is not internationally classified as hazardous, is easy to handle and has very little impact on the environment or human health. This allows radiolarian fossils to be used extensively for research, education and resource prospecting, even in institutions that cannot use the HF method due to equipment and chemical limitations.