ᴺS. [G.] glast n. “marble” (Category: Rock, Stone)
A noun appearing as G. glast “marble” in the Gnomish Lexicon of the 1910s (GL/39), probably derived from ᴱ✶ʒalast- like its cognate ᴱQ. alas (alast-) “marble” in the contemporaneous Qenya Lexicon (QL/30).
Neo-Sindarin: I think this word may be salvageable in Neo-Sindarin as ᴺS. glast, reconceived as a derivative of ᴹ√GALAS “joy, be glad”, perhaps from ᴺ✶galast- originally with the sense “thing pleasant to touch”.
References ✧ GL/24, 39