12a. Variety of medium-grained sedimentary rock composed of sand or sandstone, with high quartz content. (7). A-e-i-e. I thought Adesite, but not sure it matches the clue.
Many thanks for any help in advance.
Andesite looks good.
en.wikipedia.org/wiki/Glossary_of_geology Andesite - fine-grained igneous rock of intermediate composition. ..... Its occurrence in sands and sandstone