First, at the center of every 3x3 chunk area a random ore mix is chosen. Ore vein generation takes place as a series of steps. When viewed from a distance either via an X-Ray mod or after having removed all Stone in the area, ore Mix Veins look like large, somewhat oval-shaped clouds. In total, a vein will contain roughly equal portions of Primary and Secondary ore, slightly less Inbetween ore, and notably less Around ore. 'Around' ore appears randomly interspersed throughout the vein. The upper 2-4 levels of a vein will be almost all 'Primary' ore, the lower 2-4 levels will be almost all 'Secondary' ore, and the middle 2-4 levels will be mostly 'Inbetween' ore.

Primary, Secondary, and Inbetween ores are generated as stack ranges. Mix Veins come in four parts: Primary, Secondary, Inbetween, and Around. However, ore veins can only generate where they have Stone, Red/Black Granite, Netherrack, or End Stone that can be replaced by ore blocks. Veins can range in size from 16x16x5 up to 80x80x8 blocks, with very few and small gaps between ore blocks. Vein contents are dependent upon height and dimension, but are not dependent upon biome. Mix Veins can contain up to four different ores. Mix Veins can generate only one vein per 3x3 chunk area, however Mix Veins can contain hundreds or even thousands of blocks of ore. (GregTech Iron Ore(s) cannot be mined with a Stone pickaxe, you need Iron or Bronze to mine them.) Importantly, Small Ores can be mined at 1 mining level lower than the ores they contain, allowing a miner with a Stone-level pickaxe to obtain enough Iron to craft an Iron Pickaxe. (This can be Stone, Netherrack, Red/Black Granite, or End Stone.) Small Ores cannot be picked up with a Silktouch Pickaxe, however a Fortune Pickaxe will slightly increase their yields. Additionally, they may drop a Dust or a Dirty Dust of the Stone they were found in. When broken, they drop either a Crushed Ore, an Impure Pile of Ore Dust, or, if applicable, a Gem. They are intended as a way to get started and acquire initial tools, but are not intended to be used as primary sources of metal for machinery. Small Ores generate as semi-common single blocks. There are two types of ore generation: Small Ores and Mix Veins.

It's hard to say exactly what the visual effect looks like, but once you've seen it once or twice you come to realize that it looks wrong, and that its looking wrong is a telltale sign of the presence of ore. When viewed at steep angles, those overlays can exhibit some odd rendering behavior, either looking like black lines, white lines, or oddly transparent. (For example, for several months, the IC2 Miner could not mine GregTech ores.) The most unusual consequence of the ores being MetaTileEntities is that GregTech MTE rendering is done by combining a base texture with an overlay.

Their being TEs though has some unfortunate consequences: not all mods are prepared to deal with TE ore blocks, and so GregTech ores are not always mined by other mods' automated mining systems. This is mainly used to determine whether or not a Small Ore's drops can be enhanced by a Fortune pick. Each of these TEs contains only two variables: the internal ID of the ore, and a True/False boolean denoting whether the ore block was placed by world generation or by other means. All GregTech are non-ticking MetaTileEntities, defined not by block ID or metadata but by TileEntity data. Most mods treat their ores as single blocks, with nothing special to them except for the few that must be silktouched or can be fortune mined. GregTech ore blocks do not work exactly like other ore blocks. These patterns are compatible either by default or through configuration with almost all ores from almost all other mods, so unless explicitly noted, ore generation from other mods can and should be disabled, as GregTech will compensate. GregTech disables all Vanilla ores (except Emerald Ore, because Mojang did weird things with it) and replaces them with its own ore generation patterns.

Tile miner death