Brown Crystals is a color-led catalogue path rather than a single-material family. Recorded material labels include Jasper, Tiger Eye, Smoky Quartz, and Agate, while the shape mix includes tumbled stones, spheres, towers, and hearts. Holding the color category constant makes both material and form variation visible.
Compare the material labels first—Jasper, Tiger Eye, Smoky Quartz, and Agate—then narrow the same color path by tumbled stones, spheres, towers, and hearts. Keeping those two filters separate avoids treating a shared color as proof of shared material or form.