Tin pest related problems such as tin whiskers. At 13.2 °C (about 56 °F) and below, pure tin transforms from the silvery, ductile metallic allotrope of β-form "white tin" to the brittle, nonmetallic, α-form "grey tin" with a diamond cubic structure. The transformation is slow to initiate due to a high activation energy but the presence of germanium (or crystal structures of similar form and size) or very low temperatures of roughly −30 °C aids the initiation. There is also a large volume increase of about 27% associated with the phase change to the nonmetallic low temperature allotrope. This frequently makes tin
Anniversary to as the "traditional" list. Generally speaking, the longer the period, the more precious or durable the material associated with it. See wedding anniversary for a general list of the wedding anniversary symbols; however, there are variations in some national traditions. Furthermore, there exist numerous partially overlapping, partially contradictory lists of anniversary gifts (such as wedding stones), separate from the 'traditional' names. The concepts of a person's birthday stone and zodiac stone, by contrast, are fixed for life according to the day of the week, month, or astrological sign corresponding to the recipient's birthday. Anniversary An anniversary is the date