Chart No. Mineral [Streak] Remarks Hardness
1. METALLIC luster, WHITE color
A. Does not readily leave mark on paper but can be scratched by ordinary pocket knife
[Native silver] Shiny silver white, unless tarnished Silver-white color that tarnishes to gray, black, or yellowish brown; heavy; can be flattened when hit with hammer 2½-3
2. METALLIC or SUBMETALLIC luster, GRAY color
A. Will leave mark on paper
[Argentite] Shiny, blackish to lead gray Lead-gray color that tarnishes to dull black; knife cuts it smoothly; heavy; may occur as masses and coatings 2-2½
[Galena] Grayish black Shiny lead-gray color; heavy; cube-shaped fragments and crystals 2½
[Graphite] Black Steel-gray color; greasy feel; very soft; splits into thin flakes 1-2
B. Does not readily leave mark on paper but can be scratched by ordinary pocket knife
[Chalcocite] Grayish black Shiny lead-gray color that tarnishes to dull black; knife cuts it smoothly; may have black sooty coating; commonly occurs as compact or [granular] masses 2½-3
[Hollandite] Black Silvery-gray color; may occur as rounded masses 4-6
C. Cannot be scratched by ordinary pocket knife
[Braunite] Steel gray or black Dark steel-gray color and submetallic luster 6-6½
[Hematite] Dark reddish brown Steel-gray color; commonly occurs as granular or compact masses; shiny, scaly variety is specular [hematite]; notice streak 5½-6½ (may be softer)
[Hollandite] Black Silvery-gray color; may occur as rounded masses 4-6
3. METALLIC luster, YELLOW color
A. Does not readily leave mark on paper but can be scratched by ordinary pocket knife
[Chalcopyrite] Greenish black Brass-yellow or golden-yellow color that may tarnish and show rainbow-like colors; commonly [massive]; notice streak 3½-4
[Gold] Shiny golden yellow Shiny yellow color; extremely heavy; flattens when hit with hammer; notice streak 2½-3
B. Cannot be scratched by ordinary pocket knife
[Pyrite] Black, greenish black, or brownish black Shiny, pale golden-yellow or brass-yellow color that may tarnish; occurs as grains, as masses, or as [cubes] or other crystal shapes; notice hardness and streak 6-6½
4. METALLIC or SUBMETALLIC luster, BROWN color
A. Does not readily leave mark on paper but can be scratched by ordinary pocket knife
[Limonite] Rusty yellowish brown Dark-brown color; some specimens have a shiny black surface; notice streak 5-5½
B. Cannot be scratched by an ordinary pocket knife
[Cassiterite] Pale brown, pale yellow or white Brown; submetallic; heavy; notice streak 6-7
[Hematite] Dark reddish brown Dark brown color; commonly occurs as granular or compact masses; notice streak 5½-6½ (may be softer)
[Limonite] Rusty, yellowish brown Dark brown color; some specimens have a shiny black surface; notice streak 5-5½
5. METALLIC or SUBMETALLIC luster, BLACK color
A. Will leave mark on paper
[Argentite] Shiny, blackish to lead grey Lead-gray color that tarnishes to dull black; knife cuts it smoothly; heavy; may occur as masses and coatings 2-2½
[Graphite] Black Greasy feel; very soft; splits into thin flakes 1-2
[Pyrolusite] Black Very soft; will soil fingers; may be powdery 1-2
B. Does not readily leave mark on paper but can be scratched by an ordinary pocket knife
[Chalcocite] Grayish black Shiny lead-gray color that tarnishes to dull black; knife cuts it smoothly; may have a black sooty coating; commonly occurs as compact or granular masses 2½-3
[Hollandite] Black May occur as rounded masses 4-6
[Limonite] Rusty, yellowish brown Some specimens have shiny black surface; notice streak 5-5½
C. Cannot be scratched by an ordinary pocket knife
[Braunite] Steel gray or black Luster is submetallic 6-6½
[Cassiterite] Pale brown, pale yellow, or white Submetallic luster; heavy; notice streak 6-7
[Hematite] Dark reddish brown Notice streak; commonly occurs as granular or compact masses 5½-6½ (may be softer)
[Hollandite] Black May occur as rounded masses 4-6
[Limonite] Rusty yellowish brown Some specimens have shiny black surface; notice streak 5-5½
[Magnetite] Black Fragments cling to a magnet 6
[Pitchblende] Brownish black Brownish black, greenish black, or black; radioactive; heavy; may appear dull or greasy 5½
6. NONMETALLIC luster, WHITE color
A. Can be scratched by a fingernail
[Cerargyrite] Shiny white or gray Appears waxy; knife cuts it smoothly; turns violet brown to black when exposed to light 1-1½
[Gypsum] White Soft; occurs as crystals or as fibrous, granular, compact, or earthy masses 2
[Talc] White Knife cuts it smoothly; feels soapy or greasy; splits into thin flakes 1
B. Cannot be scratched by a fingernail but can be scratched by a copper penny
[Anhydrite] White Commonly occurs as sugary-looking masses 3-3½
[Barite] White Rather heavy; [cleavage fragments] may be flat and slab-like 3-3½
[Calcite] White Dilute hydrochloric acid fizzes on [calcite]; perfect [cleavage] in 3 directions gives rhomb-shaped fragments 3
[Celestite] White Not quite as heavy as [barite]; crystals commonly prism-shaped or flat-looking; some cleavage fragments are flat and slab-like 3-3½
[Halite] White Salty taste; dissolves in water; cube-shaped cleavage fragments 2½
C. Cannot be scratched by a copper penny but can be scratched by an ordinary pocket knife
[Anhydrite] White Commonly occurs as sugary-looking masses 3-3½
[Barite] White Rather heavy; cleavage fragments may be flat and slab-like 3-3½
[Celestite] White Not quite as heavy as barite; crystals commonly prism-shaped or flat-looking; some cleavage fragments are flat and slab-like 3-3½
[Dolomite] White Commonly occurs as granular masses and as rhomb-shaped crystals; dilute hydrochloric acid may fizz slightly on [dolomite] 3½-4
[Fluorite] White Cleavage in 4 directions can give fragments that are shaped like [octahedrons]; crystals commonly cubes 4
[Opal] White Curved, [conchoidal] [fracture]; may appear glassy, greasy, resinous, or dull; milky white and bluish-white [precious opal] shows plays of colors 5-6
D. Cannot be scratched by an ordinary pocket knife but can be scratched by [quartz]
[Feldspar] White Glassy or pearly luster; good cleavage in 2 directions that meet at an angle of 90° or near 90°; common in [granite] and [pegmatite] rocks 6
[Opal] White Curved, conchoidal fracture; may appear glassy, greasy, resinous, or dull; milky white and bluish-white precious opal shows plays of colors 5-6
[Quartz] White Curved conchoidal fracture; occurs as [milky quartz], [chert], and [chalcedony]; crystals commonly 6-sided prisms with pyramid-like ends 7
7. NONMETALLIC luster, GRAY color
A. Can be scratched by a fingernail
[Amphibole asbestos] White Made up of slender, flexible fibers that can be pulled apart 1-2½
[Cerargyrite] Shiny white or gray Appears waxy; knife cuts it smoothly; turns violet brown to black when exposed to light 1-1½
[Gypsum] White Soft; occurs as crystals or as fibrous, granular, compact, or earthy masses 2
[Sulfur] White or pale yellow Will burn with a blue flame; commonly found as crystals, crusts, or grains 1½-2½
[Talc] White Knife cuts it smoothly; feels soapy or greasy; splits into thin flakes 1
B. Cannot be scratched by a fingernail but can be scratched by a copper penny
[Amphibole asbestos] White Made up of slender, flexible fibers that can be pulled apart 1-2½
[Anhydrite] White Commonly occurs as sugary-looking masses 3-3½
[Calcite] White Dilute hydrochloric acid fizzes on calcite; perfect cleavage in 3 directions gives rhomb-shaped fragments 3
[Celestite] White Crystals commonly prism-shaped or flat-looking; some cleavage fragments are flat and slab-like 3-3½
[Halite] White Salty taste; dissolves in water; cube-shaped cleavage fragments 2½
[Sulfur] White or pale yellow Will burn with a blue flame; commonly found as crystals, crusts, or grains 1½-2½
C. Cannot be scratched by a copper penny but can be scratched by an ordinary pocket knife
[Anhydrite] White Commonly occurs as sugary-looking masses 3-3½
[Celestite] White Crystals commonly prism-shaped or flat-looking; some cleavage fragments are flat and slab-like 3-3½
[Dolomite] White Commonly occurs as granular masses and as rhomb-shaped crystals; dilute hydrochloric acid may fizz slightly on dolomite 3½-4
[Opal] White Curved, conchoidal fracture; may appear glassy, greasy, resinous, or dull 5-6
D. Cannot be scratched by an ordinary pocket knife but can be scratched by quartz
[Feldspar] White Glassy or pearly luster; good cleavage in 2 directions that meet at an angle of 90° or near 90°; common in granite and pegmatite rocks 6
[Opal] White Curved, conchoidal fracture; may appear glassy, greasy, resinous, or dull 5-6
[Quartz] White Curved conchoidal fracture; occurs as chert and chalcedony 7
8. NONMETALLIC luster, YELLOW color
A. Can be scratched by a fingernail
[Carnotite] Yellow Bright canary yellow or lemon yellow; radioactive; occurs as crusts and powdery masses 2
[Gypsum] White Yellowish; soft; occurs as crystals or as fibrous, granular, compact or earthy masses 2
[Limonite] Rusty yellowish brown Brownish-yellow color; may be soft and earthy 1+
[Muscovite] (white [mica]) White Light colored; splits into thin, flat, [transparent] sheets that will bend without breaking 2-2½
[Sulfur] White or pale yellow Will burn with a blue flame; commonly found as crystals, crusts, or grains 1½-2½
[Uranophane] Light yellow to light yellow orange Yellow to yellow-orange color; radioactive 2-3
B. Cannot be scratched by a fingernail but can be scratched by a copper penny
[Barite] White Rather heavy; cleavage fragments may be flat and slab-like 3-3½
[Calcite] White Yellowish; dilute hydrochloric acid fizzes on calcite; perfect cleavage in 3 directions gives rhomb-shaped fragments 3
[Muscovite] (white mica) White Light colored; splits into thin, flat, transparent sheets that will bend without breaking 2-2½
[Sulfur] White or pale yellow Will burn with a blue flame; commonly found as crystals, crusts, or grains 1½-2½
[Uranophane] Light yellow to light yellow orange Yellow to yellow-orange color; radioactive 2-3
C. Cannot be scratched by a copper penny but can be scratched by an ordinary pocket knife
[Barite] White Rather heavy; cleavage fragments may be flat and slab-like 3-3½
[Opal] White Curved, conchoidal fracture; may appear glassy, greasy, resinous, or dull 5-6
D. Cannot be scratched by an ordinary pocket knife but can be scratched by quartz
[Feldspar] White Glassy or pearly luster; good cleavage in 2 directions that meet at an angle of 90° or near 90° 6
[Garnet] White Commonly occurs as crystals 6½-7
[Opal] White Curved, conchoidal fracture; may appear glassy, greasy, resinous, or dull 5-6
[Quartz] White Curved conchoidal fracture; brownish-yellow smoky quartz crystals commonly 6-sided prisms with pyramid-like ends; chalcedony and [jasper] may be a shade of yellow, too 7
9. NONMETALLIC luster, BROWN color
A. Can be scratched by a fingernail
[Gypsum] White Brownish; soft; occurs as crystals or as fibrous, granular, compact or earthy masses 2
[Limonite] Rusty yellowish brown May be soft and earthy 1+
[Muscovite] (white mica) White Light colored; splits into thin, flat, transparent sheets that will bend without breaking 2-2½
[Sulfur] White or pale yellow Will burn with a blue flame; commonly found as crystals, crusts, or grains 1½-2½
B. Cannot be scratched by a fingernail but can be scratched by a copper penny
[Barite] White Rather heavy; cleavage fragments may be flat and slab-like 3-3½
[Biotite] (black mica) White Dark brown; splits into thin, flat sheets that will bend without breaking 2½-3
[Calcite] White Dilute hydrochloric acid fizzes on calcite; perfect cleavage in 3 directions gives rhomb-shaped fragments 3
[Halite] White Salty taste; dissolves in water; cube-shaped cleavage fragments 2½
[Muscovite] (white mica) White Light colored; splits into thin, flat, transparent sheets that will bend without breaking 2-2½
[Sulfur] White or pale yellow Will burn with a blue flame; commonly found as crystals, crusts, or grains 1½-2½
C. Cannot be scratched by a copper penny but can be scratched by an ordinary pocket knife
[Barite] White Rather heavy; cleavage fragments may be flat and slab-like 3-3½
[Dolomite] White Commonly occurs as granular masses and as rhomb-shaped crystals; dilute hydrochloric acid may fizz slightly on dolomite 3½-4
[Fluorite] White Cleavage in 4 directions can give fragments that are shaped like octahedrons; crystals commonly cube-shaped 4
D. Cannot be scratched by an ordinary pocket knife but can be scratched by quartz
[Cassiterite] Pale brown, pale yellow, or white Brown, reddish brown, or yellowish brown; heavy; dull to brilliant luster 6-7
[Feldspar] White Glassy or pearly luster; good cleavage in 2 directions that meet at an angle of 90° or near 90°; common in granite and pegmatite rocks 6
[Garnet] White Commonly occurs as crystals 6½-7
[Quartz] White Curved conchoidal fracture; brown smoky quartz crystals commonly 6-sided prisms with pyramid-like ends; chalcedony, chert, and jasper may be a shade brown, too 7
[Tourmaline] White Dark brown variety is [dravite]; notice hardness, striations on crystals, and triangular cross section of some crystals 7-7½
E. Cannot be scratched by quartz
[Tourmaline] White Dark brown variety is dravite; notice hardness, striations on crystals, and triangular cross section of some crystals 7-7½
10. NONMETALLIC luster, BLACK color
A. Cannot be scratched by a fingernail but can be scratched by a copper penny
[Biotite] (black mica) White Splits into thin, flat sheets that will bend without breaking 2½-3
B. Cannot be scratched by an ordinary pocket knife but can be scratched by quartz
[Garnet] White Commonly occurs as crystals 6½-7
[Quartz] White Curved conchoidal fracture; brownish-black [smoky quartz] crystals commonly 6-sided prisms with pyramid-like ends; chalcedony and chert may be black, too 7
[Tourmaline] White Black variety is [schorl]; notice hardness, striations on crystals, and triangular cross section of some crystals 7-7½
C. Cannot be scratched by quartz
[Tourmaline] White Black variety is schorl; notice hardness, striations on crystals, and triangular cross section of some crystals 7-7½
11. NONMETALLIC luster, GREEN color
A. Can be scratched by a fingernail
[Amphibole asbestos] White Made up of slender, flexible fibers that can be pulled apart 1-2½
[Cerargyrite] Shiny white or gray Light greenish color; appears waxy; knife cuts it smoothly; turns violet brown to black when exposed to light 1-1½
[Muscovite] (white mica) White Light colored; splits into thin, flat, transparent sheets that will bend without breaking 2-2½
[Sulfur] White or pale yellow Greenish; will burn with a blue flame; commonly found as crystals, crusts, or grains 1½-2½
[Talc] White Light greenish color; knife cuts it smoothly; feels soapy or greasy; splits into thin flakes 1
B. Cannot be scratched by a fingernail but can be scratched by a copper penny
[Amphibole asbestos] White Made up of slender, flexible fibers that can be pulled apart 1-2½
[Biotite] (black mica) White Dark green; splits into thin, flat, [translucent] sheets that will bend without breaking 2½-3
[Calcite] White Dilute hydrochloric acid fizzes on calcite; perfect cleavage in 3 directions gives rhomb-shaped fragments 3
[Halite] White Greenish tint; salty taste; dissolves in water; cube-shaped cleavage fragments 2½
[Muscovite] (white mica) White Light colored; splits into thin, flat, transparent sheets that will bend without breaking 2-2½
[Serpentine] White Two kinds: silky and fibrous, waxy and platy 2½-4
[Sulfur] White or pale yellow Greenish; will burn with a blue flame; commonly found as crystals, crusts, or grains 1½-2½
C. Cannot be scratched by a copper penny but can be scratched by an ordinary pocket knife
[Fluorite] White Cleavage in 4 directions can give fragments shaped like octahedrons; crystals commonly cubes 4
[Malachite] Green Bright green color; dilute hydrochloric acid will fizz on [malachite] 3½-4
[Serpentine] White Two kinds: silky and fibrous, waxy and platy 2½-4
D. Cannot be scratched by an ordinary pocket knife but can be scratched by quartz
[Feldspar] White Glassy or pearly luster; good cleavage in 2 directions that meet at an angle of 90° or near 90° 6
[Garnet] White Commonly occurs as crystals 6½-7
12. NONMETALLIC luster, BLUE color
A. Cannot be scratched by a fingernail but can be scratched by a copper penny
[Anhydrite] White Commonly occurs as sugary-looking masses 3-3½
[Barite] White Rather heavy; cleavage fragments may be flat and slab-like 3-3½
[Calcite] White Dilute hydrochloric acid fizzes on calcite; perfect cleavage in 3 directions gives rhomb-shaped fragments 3
[Celestite] White Not quite as heavy as barite; crystals commonly prism-shaped or flat-looking; some cleavage fragments are flat and slab-like 3-3½
[Halite] White Salty taste; dissolves in water; cube-shaped cleavage fragments 2½
B. Cannot be scratched by a copper penny but can be scratched by an ordinary pocket knife
[Anhydrite] White Commonly occurs as sugary-looking masses 3-3½
[Azurite] Blue Bright, intense blue color; dilute hydrochloric acid will fizz on [azurite] 3½-4
[Barite] White Rather heavy; cleavage fragments may be flat and slab-like 3-3½
[Celestite] White Not quite as heavy as barite; crystals commonly prism-shaped or flat-looking; some cleavage fragments are flat and slab-like 3-3½
[Fluorite] White Cleavage in 4 directions can give fragments that are shaped like octahedrons; crystals commonly cube-shaped 4
[Opal] White Curved, conchoidal fracture; may appear glassy, greasy, resinous, or dull; milky white and bluish-white precious opal shows plays of colors 5-6
C. Cannot be scratched by an ordinary pocket knife but can be scratched by quartz
[Feldspar] White Glassy or pearly luster; good cleavage in 2 directions that meet at an angle of 90° or near 90° 6
[Opal] White Curved, conchoidal fracture; may appear glassy, greasy, resinous, or dull; milky white and bluish-white precious opal shows plays of colors 5-6
[Quartz] White Curved conchoidal fracture; occurs as [crystalline] quartz and as bluish chalcedony 7
D. Cannot be scratched by quartz
[Topaz] White Perfect basal cleavage gives flat, plate-like fragments; notice hardness 8
13. NONMETALLIC luster, RED or PINK color
A. Can be scratched by a fingernail
[Gypsum] White Reddish; soft; occurs as crystals or as fibrous, granular, compact, or earthy masses 2
[Hematite] Dark reddish brown Brownish-red color; soft and earthy 1+
[Sulfur] White or pale yellow Reddish; will burn with blue flame; commonly found as crystals, crusts, or grains 1½-2½
B. Cannot be scratched by a fingernail but can be scratched by a copper penny
[Anhydrite] White Pinkish tint; commonly occurs as sugary-looking masses 3-3½
[Barite] White Pinkish tint; rather heavy; cleavage fragments may be flat and slab-like 3-3½
[Calcite] White Pink color; dilute hydrochloric acid fizzes on calcite; perfect cleavage in 3 directions gives rhomb-shaped fragments 3
[Cinnabar] Dark red Dark red or bright yellowish-red color; shiny, brilliant luster when pure; dull and earthy when impure; heavy 2½
[Halite] White Reddish tint; salty taste; dissolves in water; cube-shaped cleavage fragments 2½
[Sulfur] White or pale yellow Reddish; will burn with blue flame; commonly found as crystals, crusts, or grains 1½-2½
C. Cannot be scratched by a copper penny but can be scratched by an ordinary pocket knife
[Anhydrite] White Pinkish tint; commonly occurs as sugary-looking masses 3-3½
[Barite] White Pinkish tint; rather heavy; cleavage fragments may look flat and slab-like 3-3½
[Dolomite] White Pink color; commonly occurs as granular masses and as rhomb-shaped crystals; dilute hydrochloric acid may fizz slightly on dolomite 3½-4
[Fluorite] White Pink color; cleavage in 4 directions can give fragments that are shaped like octahedrons; crystals commonly cubes 4
[Opal] White Reddish color; curved, conchoidal fracture; may appear glassy, greasy, resinous, or dull 5-6
D. Cannot be scratched by an ordinary pocket knife but can be scratched by quartz
[Feldspar] White Glassy or pearly luster; good cleavage in 2 directions that meet at an angle of 90° or near 90° 6
[Garnet] White Commonly occurs as crystals 6½-7
[Opal] White Reddish color; curved, conchoidal fracture; may appear glassy, greasy, resinous, or dull 5-6
[Quartz] White Curved, conchoidal fracture; occurs as [rose quartz], as pink chert, and as [agate] and jasper 7
14. NONMETALLIC luster, PURPLE or VIOLET color
A. Cannot be scratched by a copper penny but can be scratched by an ordinary pocket knife
[Fluorite] White Cleavage in 4 directions can give fragments that are shaped like octahedrons; crystals commonly cubes 4
B. Cannot be scratched by an ordinary pocket knife but can be scratched by quartz
[Quartz], variety: [amethyst] White Curved, conchoidal fracture; amethyst crystals commonly 6-sided prisms with pyramid-like ends 7
15. NONMETALLIC luster, COLORLESS
A. Can be scratched by a fingernail
[Cerargyrite] Shiny white or gray Appears waxy; knife cuts it smoothly; turns violet brown to black when exposed to light 1-1½
[Gypsum] White Transparent [selenite] variety commonly occurs as flat, diamond-shaped crystals; splits into thin, flat sheets that will not bend without breaking 2
[Muscovite] (white mica) White Splits into thin, flat, transparent sheets that will bend without breaking 2-2½
B. Cannot be scratched by a fingernail but can be scratched by a copper penny
[Barite] White Rather heavy; cleavage fragments may be flat and slab-like 3-3½
[Calcite] White Dilute hydrochloric acid fizzes on calcite; perfect cleavage in 3 directions gives rhomb-shaped fragments 3
[Celestite] White Not quite as heavy as barite; crystals commonly prism-shaped or flat-looking; some cleavage fragments are flat and slab-like 3-3½
[Halite] White Salty taste; dissolves in water; cube-shaped cleavage fragments 2½
[Muscovite] (white mica) White Splits into thin, flat, transparent sheets that will bend without breaking 2-2½
C. Cannot be scratched by a copper penny but can be scratched by an ordinary pocket knife
[Barite] White Rather heavy; cleavage fragments may be flat and slab-like 3-3½
[Celestite] White Not quite as heavy as barite; crystals commonly prism-shaped or flat-looking; some cleavage fragments are flat and slab-like 3-3½
[Dolomite] White Commonly occurs as granular masses and as rhomb-shaped crystals; dilute hydrochloric acid may fizz slightly on dolomite 3½-4
[Fluorite] White Cleavage in 4 directions can give fragments that are shaped like octahedrons; crystals commonly cubes 4
[Opal] White Curved, conchoidal fracture; transparent [hyalite] variety resembles ice 5-6
D. Cannot be scratched by an ordinary pocket knife but can be scratched by quartz
[Opal] White Curved, conchoidal fracture; transparent hyalite variety resembles ice 5-6
[Quartz] White Curved, conchoidal fracture; [rock crystal] quartz commonly 6-sided prism with pyramid-like ends 7
E. Cannot be scratched by quartz
[Topaz] White Perfect basal cleavage gives flat, plate-like fragments; notice hardness 8

How To Use the Rock Identification Charts

In the rock identification charts on pages [40]-41, the Texas rocks described in this book are arranged in four major groups according to their texture.

1. Glassy (the rocks are smooth, dark, and shiny) 2. Compact, dull, or stony (the rocks are smooth and dull, but the individual grains are too small to be recognized) 3. [Granular] (at least some of the individual grains of the rocks are large enough to be seen without a magnifying glass) 4. Fragmental (the rocks are made up of fragments that are either loose or cemented together)

Consult Rock Chart [1], if the rock is glassy; Chart [2], if it is compact, dull, or stony; Chart [3], if it is [granular]; and Chart [4], if it is fragmental.

Two of the rock charts are subdivided. In Rock Chart [2], the compact, dull, or stony rocks are arranged according to hardness as follows:

A. Rocks that can be scratched by a fingernail B. Rocks that cannot be scratched by a fingernail but can be scratched by an ordinary pocket knife C. Rocks that cannot be scratched by an ordinary pocket knife

In Rock Chart [3], the [granular] rocks also are arranged according to hardness into:

A. Rocks that can be scratched by an ordinary pocket knife B. Rocks that cannot be scratched by an ordinary pocket knife These harder rocks are subdivided into three groups: 1. Those that have grains of about equal size 2. Those with large easily seen grains that are scattered through a mass of finer grains 3. Those rocks whose grains are arranged in layers

In the “remarks” column of the rock identification charts are included further tests that will aid you in identifying the rock.