English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The paper describes a find of volcanic glass in central Nicaragua. We investigated obsidian samples in perlite from a large profile of volcanic rocks (Cerro Tijerina) in the vicinity of the town of Matagalpa. The obsidian occurs in the form of up to 3-cm dark-coloured balls (spheres) randomly distributed in brittle grey perlite, which also has spherulitic texture. These balls, previously called marekanite, are characterised by an abundance of microphenocrysts (feldspar, biotite, amphibole, apatite and magnetite). Microprobe analysis of the homogenous glass of obsidian balls and perlite has confirmed their subalkaline, and particularly high-K calc-alkaline character (SiO2 ≥ 70 %, Na2O+K2O < Al2O3), which is typical for rhyolitic melts. A sharp contact was observed between the core and the surface layer (approx. 0.1-0.2 mm) of the obsidian balls, reflecting changes in the H2O content

Obsidian balls (marekanite) from Cerro Tijerina, central Nicaragua: petrographic investigations