text: Several allotropes of boron exist : amorphous boron is a brown powder and crystalline boron is black , extremely hard ( about 9.5 on Mohs ' scale ) , and a poor conductor at room temperature .
simplified: Two types of boron are found ( allotropes ) . Amorphous boron is a brown powder and metallic ( crystalline ) boron is black and hard and a weak conductor at room temperature .