Myrrh resin is dark brown in colour, a bit like caramel, and when burnt it produces an earthy, almost pine-like scent. It's well known for its grounding and calming properties. It's great, for example, to burn if you feel like you need to get your feet solidly back on the ground or need to remain firmly grounded whilst providing healing for others. It's also believed to have sensuous properties, and was often burnt along with other substances, such as benzoin, aloe and sandalwood, as a way of enhancing this.
Along with frankincense, myrrh was commonly mentioned in the Bible and it was one of the gifts taken by the three kings to the baby Jesus. It is regarded as a feminine scent (in contrast, frankincense is regarded as masculine). The Egyptians were also wide users of myrrh, particularly for embalming and rituals of healing and passing.