Is magma a example of a mineral that indicates that a metamorphic rock was formed in a great depth and under a extreme heat and pressure?

No, magma itself is not a mineral; it is a molten rock that can crystallize to form igneous rocks. Metamorphic rocks, on the other hand, form from existing rocks (igneous, sedimentary, or other metamorphic rocks) under extreme heat and pressure, typically deep within the Earth. The presence of certain minerals, such as garnet or kyanite, can indicate the conditions of high pressure and temperature during metamorphism.