This looks like Hematite with maybe even Orpiment 😳? It’s so strange looking. Any ideas?
By - EmLiminator
Interesting piece. It does look like it's mostly hematite or goethite. The yellow stuff on the back looks like limonite, not orpiment.
What's interesting is that the iron oxide seems to have replaced other minerals based on the shape: most of the crystals look like they were dogtooth calcite, but some others in the upper right on the first photo look more like gypsum. There are some similar pieces with goethite replacing gypsum from Santa Eulalia, Mexico ([example](https://www.mindat.org/photo-281608.html)), but not certain your piece is the same.
I feel like I've seen photos of something similar before, so maybe someone will recognize it and have a more definitive answer.
This is a reminder to flair this post in /r/whatsthisrock after it has been identified! (Under your post, click "flair" then "IDENTIFIED," then type in the rock type or mineral name.) This will help others learn and help speed up a correct identification on your request!
*I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/whatsthisrock) if you have any questions or concerns.*