Rashleighite is a mineral that is relatively rare and uncommon. Because of this, there aren't many other commonly used words that can be used as synonyms for this term. One possible option is "zincian tourmaline," which is a variety of tourmaline that contains a significant amount of zinc. Another possibility is "manganonabantite," which is a rare mineral that contains both manganese and calcium. While these terms are not necessarily interchangeable with rashleighite, they do share some similarities and may be used in similar contexts within the field of mineralogy and geology.