Ice Spike

We get an ice spike, like the one pictured below, every so often and it's a tribute to the Reverse Osmosis (RO) system that Enting Water Conditioning installed several years ago to provide us with pure and great-tasting water and ice.  Ice spikes are rare enough, but they are less likely to form when water contains impurities, which inhibit spike formation, and the RO system takes most of that out.

https://en.wikipedia.org/wiki/Ice_spike