Qenya
maril
noun. glass, crystal, crystal, glass
hyelle
noun. glass
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A noun glossed “glass, crystal” on the cover page of The Etymologies of the 1930s where it was the basis of a possible derivation of [ᴹQ.] Silmaril (EtyAC/SIL).
Conceptual Development: A similar word ᴱQ. marilla “pearl” appeared in the Qenya Lexicon and Poetic and Mythological Words of Eldarissa, again as the basis for [ᴱQ.] Silmaril (QL/59; PME/59).
Neo-Quenya: The word maril seems to be the best available Quenya word for “crystal”, and I would use it that way for purposes of Neo-Quenya.