im making volcanic soil by finding out what kind of minerals are found in it. what should i use for my base?

Question

something that will not affect the results of my experiment.
sand?
or
something else...

Answer 1

Volcanic soil is more typically derived from basalt. Basalt is composed of a variety of minerals, but most notably those of the families known as pyroxenes and amphiboles. Feldspars are present, as well. Quartz, which makes up by far most sand, is absent (because, by the time the magma cooled enough for quartz to form there wasn't any SiO2 left).

There are volcanic soils made from lava that contains free quartz (rocks such as rhyolite)as well as feldspars and some darker minerals, but these are much rarer.

Finding crushed basalt (or it's coarse-crystalline equivalent, gabbro, might be a real problem. but that would be the starting point. I doubt if there are any "basalt minerals R us" (sorry--I couldn't resist), but some local monument maker might be able to find pieces of basalt or gabbro which you could crush for the experiment.