Laboratory Four: Rock-Forming Processes and the Rock Cycle

Objectives:

• Understand what rocks are and how they form
• Understand that all rocks and rock-forming materials are part of a global rock cycle that has igneous, sedimentary and metamorphic processes and rock groups
• Infer how specific hand samples of rocks have formed in relation to the rock cycle

This lab primarily discusses the processes involved in the formation of the three primary groups of rocks, and the rock cycle, a model describing how rocks can be formed, transformed, destroyed and reformed by natural processes.

All rock-forming material comes from the Earth’s mantle, space, organisms or the decay of other rocks. Processes and environmental changes acting upon these groups produce the three main rock groups: Igneous Rocks, Sedimentary Rocks, and Metamorphic Rocks.

Rock types

Igneous – Cooling of lava to a solid form, either glass or masses of intergrown mineral crystals.

The size of the mineral grains present is dependent upon cooling time.

Sedimentary – Pieces of plants, animals or other rocks are compressed and cemented together.

As well, sedimentary rocks can form from the precipitation of mineral crystals from water.

Metamorphic – Rocks are changed, or transformed, from one form to another by intense heat,

intense pressure or the action of hot fluids.

Rock Cycle (overhead)

Rock Properties

Color – indicates what minerals may be present

Composition – what minerals make up the rock, learned about minerals in last lab

Texture – the size, shape and arrangements of parts making up a rock

Examples on page 80:

Ign: glassy, vesicular, random small or large crystals in crystalline texture

Sed: silty, sandy or coarse grained detrital (clastic), layered crystalline

Meta: equigranular (all same size), folded, foliated

Grain size – fine grained v. coarse grained, glassy or vesicular

Sorting – all the same size or different sizes

Deformation – present in metamorphic rocks, indicating a change in shape or texture

Foliations – layered alignment of mineral grains

Rock Classification (Overhead)

Using the properties discussed, rocks can be classified as igneous, sedimentary or metamorphic. You may use a sheet similar to this one, or use your observations. Consider how these rock types are formed, and the kind of textures you could expect for each of them.

Ign: Forming from cooled lava or magma, igneous rocks may have ropy, streamlined shapes or

layers, and will lack fossils and organic grains. These may have various textures; crystalline, glassy, fine-grained and vesicular.

Sed: formed from lithification or precipitation. Materials are compacted and cemented together

will appear to have a fragmental or clastic texture, and will likely be layered.

Meta: have been transformed physically and/or chemically by intense heat, pressure or chemical

action of hot fluids: the textures present will indicate deformation.