I've selected "quartz" as a hard difficulty word for Hangman. It's 6 letters long, contains only English letters, and is a real English word (a mineral). What makes this word challenging is that it contains the uncommon letters 'q' and 'z', and players might not immediately think of 'u' following 'q'. Additionally, it has only one vowel ('a'), which makes it harder to guess since players often start with vowels. The word isn't a proper noun, acronym, or made-up word, and it contains no spaces, hyphens, or special characters.