Stability of α, β, γ allotropes at different temperatures While reading about elements or compounds I often come across allotropes (or forms) being referred to as α, β, γ forms.
Examples:

Sulfur has two allotropes: α rhombic and β monoclinic. Out of these two α is considered more stable at ordinary temperatures.
$\ce{SO3}$ has three forms out of which again α is considered more stable.
α-Form of iron is considered the most stable at ordinary temperatures.

Based on this small data, it makes me think whether α forms are always in general the more stable ones? Is it true? How does this nomenclature signify stability at different temperatures?
I think most of the time, they sort according to the order which temperature the allotrope/polymorph is more stable. Let's say element Z has two allotropes A and B. A is stable below 100 °C and B is stable above 100 °C. Thus allotrope A would be denoted alpha-Z and allotrope B would be denoted beta-Z.
Gray tin (alpha-tin) and white tin (beta-tin) is an example. Gray tin is stable only below 13.2 °C and white tin is stable above this point. So that's why gray tin is called alpha-tin because it is stable at a lower temperature, and ditto with white tin. As you can see in this case the beta allotrope would be the one stable at room temperature one.
Quartz (a crystalline form of silicon dioxide) is another example. See this from Wikipedia:

Quartz exists in two forms, the normal α-quartz and the high-temperature β-&gt;quartz, both of which are chiral. The transformation from α-quartz to β-quartz &gt;takes place abruptly at 573 °C (846 K; 1,063 °F).