The relationship between an igneous rock's texture and where it was formed is that the texture depends on whether or not the rock is an extrusive rock or an intrusive rock. Those two different types of classifications for rocks tell you what the texture will be. For example, Intrusive rocks have a coarse-grained texture like granite and extrusive rocks have a fine-grained texture like basalt.
More than 700, no accurate number has been given.
The three groups are igneous, sedimentary, and metamorphic. igneous forms when magma or lava cools down. sedimentary forms when sediments (clay, sand, silt etc) gets compressed. and metamorphic forms when an igneous or sedimentary goes under very high temperatures and pressure
Look for signs of banding or layering that would be evidence of sedimentary strata. Banding also occurs in metamorphic rocks, but the bands may be very distinct in color from one another. If the rock scratches with a knife, it may be sedimentary. High silica content in some igneous rocks may prevent scratching with a knife blade.