Here's why:
* Hardness is determined by mineral composition: Metamorphic rocks are formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat and pressure. This process can change the mineral composition of the rock. Some minerals are inherently hard (like quartz), while others are softer (like talc).
* Examples of hard metamorphic rocks: Marble (formed from limestone), quartzite (formed from sandstone), and gneiss (formed from various igneous and sedimentary rocks) are all hard metamorphic rocks.
* Examples of soft metamorphic rocks: Slate (formed from shale) and schist (formed from various rocks) can be relatively soft.
So, to answer your question definitively, you need to know the specific type of metamorphic rock you're interested in.
