the hardness would be like a 25

Charles Jacob Koenig has written:

'Literature abstracts of ceramic applications of nepheline syenite' -- subject(s): Bibliography, Nepheline syenite, Syenite, Ceramics

An agpaite is any of a variety of peralkaline igneous rocks, particularly nepheline syenite or phonolite.

Nephrite is a gemstone. It begins with the letter n.

Extremely iron-rich olivine is rare, but is present in some nepheline syenite. Other minerals common in minor amounts include sodium-rich pyroxene, biotite.