During a prolonged cold spell during this year's winter in the UK, I noticed some unusual ice crystals which appeared to be "growing" out of a stone in the garden (attached picture).  The temperature had been below 0 degrees for about 10 days but most of the frost had gone from the other stones around this particular one. 

The height of the ice crystals was around 1 cm with the overal size of the stone around 5 cm although the ice covering was very patchy.  Could a porous stone create this effect when the water inside freezes and is forced out of the pores...?

This water was in a plastic sheet covering up a canoe, the water is around 10cm deep. What caused these crystals to form in this manner?

This morning I found a huge wedge shaped ice crystal formed on the suface of a garden bucket. It was frozen all around but the water inside the wedge was not frozen. There was nothing in the bucket to stimulate that particular shape to form. It was simply a bucket of water.