Stone works great to create crystals. Babies should be put besides parent to be fed, but don’t leave tender distance (one died on me when I did that). Berries can be force fed to babies, but raw meat is better (if parents aren’t used). Upgrade crafting skill. Careful putting anything you want to keep in them as they will eat it.
Gachas are essentially living lootboxes and resource farms. They will eat anything (including stone, wood, or fiber) and turb it into crystals which can drop a variety of resources including black Pearl's, organic polymer, or obsidian, among other things. They also have a rare chance to drop higher-tier crystals which turn into upgraded armor and tools