Early Quenya
alaswa
adjective. like marble
alaska
adjective. like marble
alakse
adjective. like marble
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 word in the Qenya Lexicon of the 1910s with variations alaswa, alakse, alaska glossed “like marble”, an adjectival form of ᴱQ. alas (alast-) “marble” (QL/30).
Neo-Quenya: I see no straightforward way of adapting any of these forms to Neo-Quenya, so I stick to ᴺQ. alasta as the adjectival form of “marble” instead.