↑Blake, Matthew (2008). "Opal". Tagalog English Dictionary-English Tagalog Dictionary. Bansa.org., makikita sa OpalArchived 2016-03-06 at the Wayback Machine.
↑Gaboy, Luciano L. "Opal". Gabby's Dictionary, Praktikal na Talahuluganang Ingles-Filipino ni Gabby/Gabby's Practical English-Filipino Dictionary, GabbyDictionary.com.External link in |title= (help)