Final answer:
Beryl requires the element beryllium for its formation, with beryllium being an integral part of its crystalline structure as a beryllium aluminosilicate.
Step-by-step explanation:
The element that is necessary for the formation of beryl is beryllium, as beryl is a beryllium aluminosilicate with the chemical formula Be3Al2Si6O18. The presence of beryllium is crucial because it is part of the fundamental composition of this mineral. Additionally, traces of chromium (Cr³+) can replace some of the aluminum (Al³+) ions in beryl, transforming it into an emerald with a characteristic green color. Beryllium forms primarily molecular compounds due to its small size and relatively high ionization energy, having only two valence electrons. Hence, it is the beryllium that is essential for the initial formation of beryl.