The alkaline-earth elements are highly metallic and are good conductors of electricity. They have a gray-white lustre when freshly cut but tarnish readily in air, particularly the heavier members of the group. Beryllium is sufficiently hard to scratch glass, but barium is only slightly harder than lead. The melting points (mp) and boiling points (bp) of the group are higher than those of the corresponding alkali metals; they vary in an irregular fashion, magnesium having the lowest and bp 1,090 °C and beryllium the highest. The elements crystallize in one or more of the three regular close-packed metallic crystal forms.
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