Expanded Rock Collection

45 specimens, approximately 1 1/2" x 1 1/2", includes 15 each of igneous, sedimentary and metamorphic rocks. Each category of rock is well represented and forms an integrated classroom study unit.

Expanded Rock Collection

IGNEOUS ROCKS

Rocks which have formed from the molten state are called igneous rocks. Igneous rocks that have cooled and crystallized deep beneath the surface of the earth are called INTRUSIVE or PLUTONIC rocks. Plutonic rocks usually display PHANERITIC or PORPHYRITIC texture. Rocks that were formed when lava reached the surface of the earth through fissures, vents or volcanoes are called EXTRUSIVE or VOLCANIC rocks. Volcanic rocks will usually exhibit APHANITIC texture.

PHANERITIC TEXTURE - Mineral grains of nearly equal size and visible to the naked eye.
1. PEGMATITE is a very coarse grained plutonic rock with a similar composition to granite.
2. GRANITE is a crystalline rock consisting of potassium feldspar and quartz with hornblende and mica as common accessory minerals.
3. GRANODIORITE is a crystalline rock consisting of quartz, plagioclase feldspar, potassic feldspar, hornblende, and biotite.
4. DIORITE is a crystalline rock consisting of plagioclase feldspar and hornblende,biotite or augite.
5. GABBRO is a crystalline plutonic rock consisting of plagioclase with minor amounts of augite.
6. SYENITE is a plutonic rock consisting principally of plagioclase feldspar and minor amounts of hornblende and biotite.

PORPHYRITIC TEXTURE - Mineral grains of two distinct sizes.
7. BASALT PORPHYRY is a dark colored rock containing feldspar crystals in an aphanitic groundmass of plagioclase feldspar and hornblende.
8. MONZONITE PORPHYRY is a light colored rock containing approximately equal amounts of orthoclase and plagioclase feldspar and little or no quartz and augite.

APHANITIC TEXTURE (Micro crystalline) - Mineral grains too small to be seen by the naked eye.
9. RHYOLITE is a light colored rock consisting of micro crystalline potassium feldspar, quartz, and minor accessory minerals.
10. ANDESITE is a light colored rock consisting of plagioclase feldspar and hornblende, biotite or augite.
11. TRACHYTE is composed of potassium feldspar, minor plagioclase feldspar, and accessory hornblende.

APHANITIC TEXTURE (Glassy)
12. OBSIDIAN is a glassy volcanic rock formed by the rapid cooling of rhyolitic lava's.
13. PITCHSTONE is formed by the rapid cooling of rhyolitic laves, and has a resinous or pitchy appearance.
14. PUMICE is a light colored volcanic rock of rhyolitic composition; the texture results from bubbles formed by escaping gasses.
15. SCORIA is a dark colored volcanic rock of basaltic composition with a porous texture due to escaping gasses

METAMORPHIC ROCKS

Metamorphic rocks may be formed by different processes. Generally they are recrystallized in the solid state by pressure and heat and may be influenced by the introduction of chemically active solutions. Igneous, sedimentary, and preexisting metamorphic rocks may become metamorphic rocks. The change may be partial and some of the original characteristics retained, or it may be so complete that new minerals are formed and the texture altered.

FOLIATED ROCKS

16. GNEISS may be formed form granites or sedimentary rocks and typically shows layering of mica, quartz and feldspar.
17. GRAPHITE SCHIST is composed almost completely of the mineral graphite having a layered texture.
18. MUSCOVITE SCHIST is composed of small layered flakes of muscovite.
19. GARNET MICA SCHIST is composed primarily of small flakes of mica with larger crystals of garnet.
20 .CHLORITE SCHIST is composed almost completely of the mineral chlorite having a layered texture.
21. SLATE is metamorphosed from shale. It has an extremely fine texture and splits cleanly along its rock planes.
22. PHYLLITE is intermediate between schist and slate. A silky sheen is characteristic of phyllite.
23. SOAPSTONE is a rock rich in talc. When layering is apparent, it is called a talc schist.

NONFOLIATED ROCKS

24. QUARTZITE is a metamorphosed sandstone which is partially recrystallized.
25. SERPENTINITE is a metamorphosed serpentine rock derived from the alteration of olivine and pyroxene or impure limestone.
26. EPIDOSITE is composed primarily of the minerals epidote and quartz.
27. MARBLE is a recrystallized limestone (calcite).
28. ANTHRACITE is a metamorphosed bituminous coal.
29. AMPHIBOLITE consists of amphiboles and plagioclase feldspar. If may also show foliation.
30. HORNFELS is usually a fine-grained nonfoliated rock and may retain some of its sedimentary structure.

SEDIMENTARY ROCKS

Rocks derived from preexisting rocks through the processes of erosion, followed by compaction, or chemical precipitation are called sedimentary rocks. Sedimentary rocks are grouped in three categories, clastic, chemical, and organic. Clastic rocks are formed by mechanical weathering. Weathering produces gravels, sands, and silts which are then cemented together by natural cements such as silica, iron oxides, and various carbonates to form clastic rocks. In the processes of weathering, rocks or parts of rocks may be dissolved. As the solution cools or evaporates the solid portion is deposited as a precipitate. Rocks formed in this way are referred to as chemical rocks. Rocks which are formed form the compaction of plant remains are termed organic rocks.

CLASTIC ROCKS

31. CONGLOMERATE is composed of reconsolidated gravel and sand particles.
32. BRECCIA is composed or angular fragments of rocks cemented together.
33. SANDSTONE is essentially sand-size particles cemented together by calcite, silica, or iron oxides.
34. QUARTZ SANDSTONE is a sandstone composed of quartz grains cemented together by silica.
35. ARKOSE is composed essentially of quartz and feldspar particles with smaller amounts of mica.
36. SHALE is a sediment is which the constituent particles are predominantly of clay size.
37. OIL SHALE contains solid hydrocarbons and plant remains. Petroleum-like products can be distilled from the rock.

CHEMICAL ROCKS

38. LIMESTONE consists mainly of calcium carbonate which will yield lime when "burned".
39. ARAGONITE is deposited by hot springs and in carbonated bodies of water.
40. FOSSIL LIMESTONE is a limestone formed form shell fragments deposited in swamp-like areas.
41. DOLOMITE is composed largely of calcium magnesium carbonate and is often found interlayered with limestone.
42. ROCK GYPSUM is composed of calcium sulfate deposited between layers of other sedimentary rocks.
43. CALCAREOUS TUFA is composed of calcium carbonate deposited for solution in waters of springs, lakes, or from percolating ground water.
44. ROCK SALT is crystalline and granular aggregates of sodium chloride deposited form evaporating sea waters.

ORGANIC ROCKS

45. BITUMINOUS COAL is known as "soft coal". It is high in carbonaceous matter and contains between 15 to 50 percent volatile matter.