Crystal structure "white tin" respectively. Two more allotropes, γ and σ, exist at temperatures above 161 °C and pressures above several GPa. White tin is metallic, and is the stable crystalline form at or above room temperature. Below 13.2 °C, tin exists in the gray form, which has a diamond cubic crystal structure, similar to diamond, silicon or germanium. Gray tin has no metallic properties at all, is a dull gray powdery material, and has few uses, other than a few specialized semiconductor applications. Although the α–β transformation temperature of tin is nominally 13.2 °C, impurities (e.g. Al, Zn, etc.) lower the
Gift white elephant. One means of reducing the mismatch between the buyer and receivers' tastes is advance coordination, often undertaken in the form of a wedding registry or Christmas list. Wedding registries in particular are often kept at a single store, which can designate the exact items to be purchased (resulting in matching housewares), and to coordinate purchases so the same gift is not purchased by different guests. One study found that wedding guests who departed from the registry typically did so because they wished to signal a closer relationship to the couple by personalizing a gift, and also found that