The most important thing to learn about the OSI model is what it really represents. Pretend you're an operating system on a network. Your network card, operating at layers 1 and 2, will notify you when there's data available. The driver handles the shedding of the layer 2 frame, which reveals a bright, shiny layer 3 packet inside (hopefully).
Used with permission. Agate is a variety of chalcedony, a cryptocrystalline form of quartz. Translucency, patterns of color, or moss-like inclusions may distinguish this stone from other forms of chalcedony. Agates can show a wide variety of vivid, multiple colors.
Crystal Forms and Aggregates. Agate is a banded microcrystalline form of the mineral Quartz, and does not occur in visible crystals. It occurs in nodules, in massive form, as botryoidal, mammilary, and stalactitic formations, as smooth rounded pebbles, as amygdules, and as the linings of geodes.