Possible Clues:

• Stupid-sounding moggy beginning to eat salt
• Quartz, e.g
• Quartz, mica or talc
• Kind of compound comprising most of the earth's crust
• 'Mineral salt', said foolish girl
• In the glass you'll see how 1 across the girl sounds (8)
• How silly Catherine sounds in the glass
• The lass in the glass is so foolish, by the sound of it
• Mica or quartz
• Sounds as if the stupid lass is like glass