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
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
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
5. GABBRO is a crystalline plutonic rock consisting of plagioclase with minor amounts of
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
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
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 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
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
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
20 .CHLORITE SCHIST is composed almost completely of the mineral chlorite having a layered
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
23. SOAPSTONE is a rock rich in talc. When layering is apparent, it is called a talc
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
30. HORNFELS is usually a fine-grained nonfoliated rock and may retain some of its
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.
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
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
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.
38. LIMESTONE consists mainly of calcium carbonate which will yield lime when
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
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
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.
45. BITUMINOUS COAL is known as "soft coal". It is high in carbonaceous matter
and contains between 15 to 50 percent volatile matter.