Abstract
Agate nodules from Kerrouchen (Khenifra Province, Meknes-Tafilalet Region) in Morocco occur in Triassic basalts and reach up to 30 cm in diameter. Monocentric, banded agates—mainly in pastel pink, grey, white and yellow—with infiltration canals (osculum) are observed. Raman microspectroscopy revealed that the agates mainly consist of low quartz and subordinately moganite with distinctive 460 and 501 cm−1 marker bands, respectively. Linear mapping indicated that moganite mainly concentrates in grey zones of the monocentric agate nodules. The other types, polycentric and pseudostalactitic agates, are usually brown and red and contain minerals such as hematite and goethite. They form both regular and irregular mosaics rich in ornamentation. Occasionally, aggregates of copper sulphides or titanium oxides (rutile) can also be observed. These minerals are sometimes accompanied by carbonaceous material marked by 1320 and 1585 cm−1 Raman bands. It seems that formation of agates from Kerrouchen was induced by Si-rich and Fe-moderate fluids. Copper sulphides, rutile, and carbonates (possibly calcite) were most likely incorporated during post-magmatic processes. The origin of solid bitumen can be the result of hydrothermal or hypergenic processes.
Highlights
The crystallization of agates worldwide has proceeded for millions of years
This study described, in detail, the internal texture of the agates as well as number and character of solid inclusions found in them
The agates can be collected on the mountain slopes, in the agricultural fields, as well as along the road running from Bouma to Kerrouchen
Summary
The crystallization of agates worldwide has proceeded for millions of years. The oldest gems were found in Pilbara rock formations (3500–2700 Ma) and the youngest originated from volcanic tuffs from the Yucca Mt. in the USA (13 Ma) [1]. Formation of agates takes place in volcanic rocks, hydrothermal veins, or in sediments. Agate genesis in acidic volcanic host rocks starts with the formation of lithophysae (high-temperature crystallization domains). The agate geodes from Kerrouchen are unique by their variety of patterns and morphological structures. They are mainly monocentric, subordinately polycentric to pseudostalactitic. The “agate fever” did not start there until of the 20th century Such interest in Moroccan agates by collectors worldwide has not resulted in the increased amounts of the scientific publications. In the present study, continuing the research on Moroccan agates, the distribution of different silica phases in rhythmically zoned agates from Kerrouchen, together with the characteristic of solid inclusions occurring in their coloured zones, are presented. Supported by Raman microspectroscopy (RS), and X-ray fluorescence analysis (XRF)
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