TY - JOUR

T1 - Agate genesis

T2 - A continuing enigma

AU - Moxon, Terry

AU - Palyanova, Galina

N1 - Funding Information: Funding: This research was funded by the Ministry of Science and Higher Education of the Russian Federation within the framework of the state assignment of the Sobolev Institute of Geology and Mineralogy of Siberian Branch of Russian Academy of Sciences (topic no. 0330-2016-0001). Publisher Copyright: © 2020 by the authors. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/11

Y1 - 2020/11

N2 - This review covers the last 250 years of major scientific contributions on the genesis of agates found in basic igneous host rocks. From 1770 to 1955, the genesis question was frequently limited to discussions based on observations on host rock and agate thick sections. Over the next 25 years, experimental investigations examined phase transformations when silica glass and various forms of amorphous silica were heated to high temperatures. This work demonstrated that the change from the amorphous state into chalcedony was likely to be a multi-stage process. The last 40 years has seen modern scientific instrumentation play a key role in identifying the physical and chemical properties of agate. The outcome of this work has allowed limited evidence-based comment on the conditions of agate formation. There is a general consensus that agates in these basic igneous hosts form at <100◦C. However, the silica source and the nature of the initial deposit remain to be proven.

AB - This review covers the last 250 years of major scientific contributions on the genesis of agates found in basic igneous host rocks. From 1770 to 1955, the genesis question was frequently limited to discussions based on observations on host rock and agate thick sections. Over the next 25 years, experimental investigations examined phase transformations when silica glass and various forms of amorphous silica were heated to high temperatures. This work demonstrated that the change from the amorphous state into chalcedony was likely to be a multi-stage process. The last 40 years has seen modern scientific instrumentation play a key role in identifying the physical and chemical properties of agate. The outcome of this work has allowed limited evidence-based comment on the conditions of agate formation. There is a general consensus that agates in these basic igneous hosts form at <100◦C. However, the silica source and the nature of the initial deposit remain to be proven.

KW - Agate

KW - Age

KW - Chalcedony

KW - Crystallite growth

KW - Genesis

KW - Moganite

KW - XRD

KW - CRYSTALLIZATION

KW - crystallite growth

KW - SILICA POLYMORPH

KW - YUCCA MOUNTAIN

KW - SKELETON COAST

KW - moganite

KW - X-RAY-DIFFRACTION

KW - VOLCANIC-ROCKS

KW - agate

KW - genesis

KW - ORIGIN

KW - MICROCRYSTALLINE QUARTZ

KW - KAROO VOLCANICS

KW - chalcedony

KW - age

KW - OXYGEN-ISOTOPE ZONATION

UR - http://www.scopus.com/inward/record.url?scp=85094919892&partnerID=8YFLogxK

U2 - 10.3390/min10110953

DO - 10.3390/min10110953

M3 - Review article

AN - SCOPUS:85094919892

VL - 10

SP - 1

EP - 26

JO - Minerals

JF - Minerals

SN - 2075-163X

IS - 11

M1 - 953

ER -