4.3b giant covalent network

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 Allotropes: are same element but in different forms.

Carbon, silicon, and silicon dioxide form giant covalent molecules.

Carbon occurs as allotropes with different bonding within giant molecules – diamond, graphite, fullerene (C₆₀, Buckingham fullerene), and graphene. Note that Fullerene is the ONLY one that is molecular (NOT covalent network solid).​

By NBALAKRISHNAN1 in chemisfunblog

Sillicon - You also have to know two types of sillicon giant covalent network: Si and SiO₂. It is important because of SiO₂ is sand/rock/ used to make glass and also computer stuffs (Sillicon valley) 

one Si is bonded to 4 oxygen in a tetrahedral (sp3) structure

In 3D, glass (SiO₂) looks like diamond. Hence, shiny!

Si has so many allotropes (some are doped with other elements) with countless uses and still under intense research. Example crystalline silicon is used to make computer chips and solar panels.

You are not expected to know all these Si allotropes but when given an example, you need to be able to recognize:

1. They are giant covalent network
2. The geometry (tetrahedral or trigonal planar) and bond angle
3. HL: The hybridization

Example just for fun: Nature.com summary

https://www.nature.com/articles/am201082