Echinus (e-KI-nus) Geyser is the largest acidic geyser in the world, making it a star in an extremely rare class. Its water has a pH of 3.63 and temperatures around 176F/80C. The name comes from the spiny mineral formations around its vent, which were thought by the US Geological Survey party that named it in the 1870s to resemble a sea urchin of the class echinoidea. It’s found in the Norris Geyser Basin, which is more north than south and more west than east in the park.

The hat Echinus looks more like a sea urchin without the spines: it borrows the aesthetic of the urchin’s segmentation and knobbly surface to make a hat of striking visual symmetry and textural appeal. The pattern is straightforward and easy to remember; the hat itself is a quick knit that makes a great gift that looks good inside out or outside in.