Slate (writing) Slate (writing) A slate is a thin piece of hard flat material, such as the rock also called slate, that is used as a medium for writing. The rock is “a metamorphic rock created by the recrystallization of the minerals in shale from clay to parallel-aligned, flat, flake-like minerals such as mica”. The writing slate consisted of a piece of slate, typically either 4x6 inches or 7x10 inches, encased in a wooden frame. A precise date range for writing slates of this type has not been established. Usually, a piece of cloth or slate sponge was used to clean it
Physical change an alloy can be difficult and may require chemical processing – making an alloy is an example of a physical change that cannot readily be undone by physical means. Alloys where mercury is one of the metals can be separated physically by melting the alloy and boiling the mercury off as a vapour. Physical change Physical changes are changes affecting the form of a chemical substance, but not its chemical composition. Physical changes are used to separate mixtures into their component compounds, but can not usually be used to separate compounds into chemical elements or simpler compounds. Physical changes occur