Star-shaped crystals form on stream ice when it gets very cold – in the single digits F. The smaller shapes are stars or crosses, but some forms are masses of pointed crystals. The snow at the edge of a stream can form dense mats of these crystals, and the icy surface can have clusters of starry crystals. Here are a few crystal islands on dark stream ice:
Frost crystals grow in different shapes, depending in part on the temperature. On one morning, I found the snowflake-like hexagonal plates you see in one of these images. All of the leaves around this one were covered with them. On another morning, I found rod-like frost crystals. When you get close enough, you can see that the rods are pipes of ice, hollow inside. Click an image to see it in a larger size:
This sort of image – frost on leaves scattered in the ground – is the sort of thing I take in late fall. In early January when I took these, the ground was still bare, and the leaf litter was still visible. Hard to imagine that now, with three or four feet of snow on the ground.
An isolated oak in a foggy California field – there’s a bit of sun shining on a few of the rows of whatever was coming up:
Frost crystals that formed under a leaf on frozen stream:
Taken on a really cold (0 degrees F) morning. The fern-like crystals on the right side of the leaf only form when it gets very cold, down in the single digits. I’ve seen crystals around a leaf like this, but the holes in the leaf and the profusion of crystals give this an unusual look.