Final answer:
Expanded shale is created by heating materials such as sandstones, red shales, and siltstones in a rotary kiln. Other rocks can also be used, and the presence of new minerals during metamorphism provides insights into the conditions of the terrane.
Step-by-step explanation:
Expanded shale is a lightweight aggregate that is often used in construction and horticultural applications. It is produced by heating shale in a rotary kiln at high temperatures, which causes the material to expand or 'puff up.' This process gives the material its unique porous structure and lightweight characteristics. Materials used in the production of expanded shale include the following:
- Sandstones
- Red shales
- Siltstones
In addition to those materials, there are also many other geological formations and rock types that could potentially be used to create expanded shale. Some examples include Upper Lias-Dogger shale and limestone, Lower Lias limestone and dolomite, Triassic red shale, salt, and basalt, as well as Pre-Mesozoic basement rocks. Notably, during the metamorphism stage, rocks with a shale protolith will always have quartz, feldspar, and muscovite mica, and the development of new minerals such as chlorite, biotite, and the aluminosilicate polymorphs like kyanite and sillimanite can be indicative of the pressure-temperature conditions for that terrane.