Table of Contents
The various minerals have been described individually, so that any mineral specimen may be compared with a careful description of that mineral. The prospector’s task is to discover valuable minerals; and to be proficient in this, he must be practised in their identification. The best method of obtaining the requisite experience is to work in a systematic way with selected mineral specimens, the names of which are unknown to the student. For this purpose, mineral tables have been prepared, by means of which the identification of minerals may be conducted in an orderly manner. Such a table follows, and the proper method of using it will now be explained.
How to Use the Mineral Identification Tables
First note the luster, and then place the specimen in one of the two great classes:
- Minerals of Metallic Luster
- Minerals of Non-Metallic Luster
Minerals having a doubtful luster will be found in both classes. The search has now been restricted to one of these two classes. In the metallic-luster class, the search is further narrowed by determining the color of the specimen; and in the non-metallic luster class, the color of the powder makes two divisions. By continuing this principle of subdivision according to some property, either the name of the mineral is reached or a small subdivision is reached that contains a few minerals not distinguishable without making laboratory tests.
Since a few minerals are attracted by a magnet, the blade of the knife should be kept magnetized, so that this property may be tested. This may be done by rubbing the blade eight or ten times from heel to point against one pole of a magnet, or by drawing the blade a few times along the armature of a dynamo in motion, but taking care, in either case, always to move the blade in the same direction.
To practise the use of the table, take a certain unnamed specimen. Note its luster, metallic; therefore it belongs to Class I. Its color is yellowish, which puts it in Division A. Try to scratch it with the knife point; it is very hard, and the specimen is thus narrowed down to the small group containing pyrite and marcasite. These two minerals are of the same composition, and are hard to distinguish one from the other. Try the taste. Pyrite usually has no taste, but marcasite is likely to taste slightly sour and inky. This specimen is pyrite, and it should now be compared with the description given.
Take another unnamed mineral. Its metallic luster puts it in Class I. Note its color, black; this puts it in Division E. Try its hardness with a knife it is easily powdered, and so belongs to Group 2 of Division E. Try marking white paper with the specimen ; it makes a mark like that of a lead pencil, and it is either graphite or molybdenite. Try the weight; it feels light, and the specimen is therefore graphite. Confirm this by rubbing the mark with the finger until it is spread out thin. It is still gray and shows no greenish shade.
Next take an unnamed mineral with non-metallic luster which puts it in Class II. Try the color of its powder; it is distinctly colored, which puts it in Division A. The powder is brownish yellow, which puts it in Group 2 or Group 3. The specimen is rusty colored, which answers to the description of limonite. Confirm by reading on Limonite.
Now practise with another unnamed mineral whose luster is non-metallic, belonging in Class II. Powder it a little with the point of the knife; the powder is white, which puts the mineral in Division B; when making the powder, you noticed that the mineral was hard to scratch with the knife; it therefore belongs to Group 1 of Division B. The cleavage is distinct, which puts the mineral in Sub-division (b) and since the specimen feels light, it is to be placed in Subdivision (3). (Note that the differences in weight in subdivision (b) are not easily noticeable). The description of feldspar answers best to the appearance of the specimen.
Consider another unnamed mineral, luster, non- metallic; therefore, look in Class II. Powder it with the point of the knife; since powder is white, go to Division B. When making the powder, you noticed that the mineral was easy to scratch; go to Group 2. Heft the specimen; it feels light; hence, go to subdivision (a) Compare the hardness with that of the named specimen, calcite; it is as hard as calcite. Break a piece into small fragments, and note the cleavage; remarkably perfect, as shown by the brilliance of the surfaces. Note also the shape of the pieces as regards the corners and edges; the cleavage is called rhombohedral. These points, and the white color, correspond to the mineral calcite; but it is rather hard to distinguish between calcite, dolomite, and magnesite without laboratory tests.
Now consider an unnamed specimen whose non-metallic luster puts it in Class II; its white powder in Division B; its softness, in Group 2; and its lightness, in Subdivision (a). Compare its softness with that of calcite; it is softer; hence, go to (2), and read the descriptions carefully. That of gypsum corresponds best. In Group (2), the minerals are hard to distinguish by the simple tests used in this Table; the most experienced mineralogist may need to use laboratory tests to identify them.
MINERALS OF METALLIC LUSTER
A. Yellow or Yellowish Color
NOT SCRATCHED WITH KNIFE
Brass-yellow; powder, grayish-black; crystallizes in cubes, octahedrons, etc. Pyrite
Light yellow or nearly white; powder, grayish black; inky, sour, taste; forms wedge-shaped crystals. Marcasite
CAN BE SCRATCHED WITH KNIFE
Brass-yellow, often with many colored tarnish; powder, greenish-black or dark green. Copper Pyrites
Bronze-yellow, bronze-brown, or yellowish-gray; powder, black; magnetic. Pyrrhotite
Pale yellow; powder, gray; brittle. Calaverite
Golden yellow; does not powder, but spreads out. Gold
B. Red or Reddish Color
Copper-red; does not powder, but spreads out. Copper
Pale copper-red; powder, brownish- black; very heavy; H = 5 to 5.5. Niccolite
Copper-red, rosy shade; powder, reddish-brown; very heavy; hard. Breithauptite
Brownish or grayish-red; powder, red; heavy. Hematite
Brown-red when fresh, tarnishes to purple, etc.; powder, grayish-black. Bornite
Bright red or brownish-red; luster, near- metallic; powder, vermilion red; very heavy; soft. Cinnabar
Bright red or reddish-black; luster, near- metallic; powder, brownish-red, shining; heavy; soft. Cuprite
Reddish-black or black; luster, near-metallic; powder, purple red; heavy; soft. Pyrargyrite
Vermilion-red; luster, near-metallic; powder, vermilion-red. Proustite
Gray Color
HARD TO SCRATCH
Steel-gray; powder, dull red; sometimes micaceous, then seems soft. Hematite
Tin-white to steel-gray; powder, grayish black. Yellow tinge; crystals grooved. Mispickel
Blue tinge. Smaltite
EASY TO SCRATCH
(a) Dark Gray to Nearly Black
Powder, gray-black; rather sectile; cleavage, poor. Chalcocite
Powder, gray-black; brittle; no cleavage. Tetrahedrite
Powder, iron-black; slightly sectile; no cleavage. Petzite
Perfectly sectile; shiny where cut or rubbed. Argentite
Makes clean mark on white paper, gray when spread out by rubbing with finger; light. Graphite
(b) Lead-Gray
Makes clean mark on white paper, greenish when spread out by rubbing with finger; heavy. Molybdenite
Powder, lead-gray; brittle; cubic cleavage, very perfect. Galena
Powder, lead-gray; rather sectile; cleavage perfect, but often in steaks. Stibnite
Powder, lead-gray; somewhat sectile; often
yellowish or many-colored tarnish; cleavage, perfect. Bismuthinite
Powder, light gray; black tarnish; brittle.
Powder, iron-black; somewhat sectile; cleavage, poor. Arsenic
Powder, grayish-black; brittle; often needle-like crystals; cleavage, perfect Jamesonite
Powder, grayish-black; brittle; cleavage, poor. Bournonite
White Color
HARD TO SCRATCH
Silver-white to pale gray; powder, grayish-black; very heavy.
Yellow tinge; crystals grooved. Mispickel
Blue tinge. Smaltite
EASY TO SCRATCH
Malleable; may have brown or black tarnish. Silver
Sectile; rather hard. Dyscrasite
Sectile; softer; slightly reddish tint; very perfect cleavage. Bismuth
Brittle; sometimes yellowish; powder, steel-gray; cleavage, perfect. Sylvanite
Brittle; sometimes pale yellow; powder, yellowish-gray or greenish-gray; no cleavage. Calaverite
Black Color
HARD TO SCRATCH
(a) Strongly Magnetic
Powder, black. Magnetite
(b) Slightly Magnetic or Non-Magnetic
Powder, red. Hematite
Powder, brown-red, dark brown, or black; no cleavage; slightly magnetic. Ilmenite
Powder, brown; no cleavage; seldom magnetic, and then very slightly. Chromite
Powder, brownish, grayish, or white; imperfect cleavage; very heavy; very hard. Tinstone
Powder, dark brown; no cleavage; slightly magnetic; like magnetite. Franklinite
Powder, brownish-black, shiny; luster, near-metallic; no cleavage; non-magnetic. Psilomelane
Powder, brownish-black, grayish or olive-green, a little shiny; luster, near-metallic; no cleavage; non-magnetic; looks like black pitch; very heavy. Pitchblende
Powder, nearly black; cleavage, very perfect; sometimes slightly magnetic; very heavy; color usually brown-black; luster, near-metallic. Wolframite
EASY TO SCRATCH
(a) Makes Clean Mark on Paper
Gray mark; mineral is light. Graphite
Bluish-gray mark, slightly green when rubbed; mineral is heavy. Molybdenite
(b) Too Hard to Make Clean Mark on Paper
Powder, black; brittle; fibrous or granular. Pyrolusite
Powder, brown; brittle; luster, near- metallic; cleavage, very perfect. Zinc Blende
Powder, dark lead-gray; perfectly sectile. Argentite
Powder, black; very heavy. Coloradoite
Powder, red; heavy. Pyrargyrite
MINERALS OF NON-METALLIC LUSTER
A. Powder Distinctly Colored
POWDER BLACK OR BROWN-BLACK
Coal-black; soft; light; very brittle. Coal
Brown to dull black; earthy, like bog iron. Bog Manganese
Powder, black, brown red or dark brown; color, black; hard; no cleavage; slightly magnetic. Ilmenite
Luster, near-metallic; very hard; cleavage, perfect. Braunite
Luster, near-metallic; hard. Psilomelane
Luster near-metallic; pitchy; no cleavage; very heavy. Pitchblende
Like pitchblende, but harder; not so heavy. Euxenite
POWDER BROWN
Not scratched by knife; very heavy; color, black or brown; cleavage, poor. Tinstone
Hard to scratch; heavy; color, black; no cleavage. Chromite
Hard to scratch; color, black; powder, brown-red, dark brown or black; no cleavage; slightly magnetic. Ilmenite
Easier to scratch; color, black or brown; luster, resinous; cleavage, perfect. Zinc Blende
Soft or hard; color, brown; no cleavage. Limonite
Harder to scratch; color, black or brown; luster, near metallic; like zinc blende, but harder and heavier. Wolframite
Not scratched or very hard to scratch; color, reddish-brown or red; luster, near-metallic: fairly heavy; cleavage, distinct. Rutile
POWDER, YELLOW
Color, dull brown, brownish-yellow, or yellow; powder, brownish-yellow; no cleavage. Limonite
Color, deep red or orange-yellow; powder, orange-yellow; cleavage, perfect. Zincite
Color, canary-yellow; powder, canary-yellow. Carnotite
POWDER, RED
Color, brick-red; powder, red or redish-brown; earthy. Hematite
Color, cochineal-red; powder, vermilion-red; somewhat sectile. Cinnabar
Color cochineal-red; powder, brownish-red, shiny; crystals or earthy. Cuprite
Color, vermilion red; powder, same; transparent or nearly so. Proustite
POWDER, GREEN
Color, green; fairly hard; rather heavy. Malachite
Color, light apple-green; soft; light. Garnierite
6. POWDER, BLUE
Color, azure-blue; fairly hard Azurite
Powder, White or Faintly Colored
Hard to Scrap or not Scratched
(a) Cleavage, None of indistinct
Color, white, amethyst or smoky, etc.; luster, glassy; light; crystals, hexagonal. Quartz
Color, black, brown, or green; luster, glassy; light; crystals, triangular prisms, grooved. Tourmaline
Color, garnet-red, brown, or green; luster, glassy; fairly heavy; crystals, roundish. Garnet
Color, black, brown, gray, or white; luster, adamantine; very heavy; crystals, tetragonal. Tinstone
Color, yellowish or brown; luster, adamantine; heavy; crystals, tetragonal; harder than quartz. Zircon
Color, green, blue, yellow, or white; luster, glassy; light; crystals, hexagonal; harder than quartz. Beryl
(b) Cleavage Distinct
(1) Rather Heavy
H=10; G=3.5; cleavage, very perfect; roundish crystals; faces curved. Diamond
H=9; G=4; cleavage, good (parting); crystals, hexagonal. Corundum
H = 8; G=3.5; cleavage, very perfect; crystals, grooved; color, yellow. Topaz
H = 5 to 5.5; G=3.5; cleavage, fair; crystals; flat or wedge-like; color, brown. Sphene
(2) Not so Heavy
H = 6.5; color, yellowish green or brownish green; crystals mostly long. Epidote
H =6.5; color, olive-green; crystals roundish. Olivine
H = 5.5; cleavage pieces with angles of 56° and 124°. Hornblende
H = 5.5; cleavage pieces with angles nearly 90°. Pyroxene
(3) Light
Cleavage, perfect, angles 90° or nearly 90°; luster, rather pearly. Feldspar
Cleavage, fair, angles 90°; luster, rather glassy; cleavage surface fibrous looking. Scapolite
Cleavage, only fair; color, blue, etc. Sodalite
Cleavage, good; color, white. Nepheline
2. Easier to Scratch
(a) Light (G = 2.7 to 3.5)
(1) Hard as Calcite or Harder
H =3; cleavage, remarkably perfect, pieces rhombohedral; color, white. Calcite
H=3.5; cleavage, perfect, pieces rhombohedral; color, white. Dolomite
H=3.5; cleavage, perfect, pieces rhombohedral; color, pink. Rhodocrosite
H=4; cleavage, perfect, pieces rhombohedral; sometimes like porcelain; color, white. Magnesite
H=4; cleavage, perfect, with some faces equilateral triangles; color, white, green, or violet-blue, Fluorspar
H=4.5 to 5; cleavage, perfect; color, white, sometimes with pale blue or green tint. Calamine
H = 5; crystals, hexagonal; cleavage, imperfect; color, green or brown, etc. Apatite
H = 2.5 to 4; not crystalline; fracture, conchoidal or splintery. Serpentine
(2) Softer than Calcite
H= 2.5 to 4 (see above). Serpentine
H= 2.5; looks like ice, especially if wet. Cryolite
H= 2 to 3, but feels softer because of easy splitting; cleavage very perfect, into thin, elastic leaves. Mica
H = 2; color, white; glistening; cleavage, very perfect; not elastic. Gypsum
H = 1 to 2; color, green, etc.; fine grained or in scales like mica; not elastic. Chlorite
H = 1; color, white, pale green, or gray; soapy feel. Talc
Soft, powdery; clayey smell when breathed on; plastic when wet. China Clay
H = 1 to 3; color, white, yellow, brown, or red; clayey smell when breathed upon; usually oolitic, that is, with round grains like fish eggs. Bauxite
(b) Heavy (G = 3.7 to 6.5)
H=3; G=6.3; cleavage, distinct; very brittle; color, white, slightly tinted. Anglesite
H=3; G=6.5; cleavage, distinct; very brittle; color, white; luster, brilliant, like diamond. Cerussite
H =2.5 to 3.5; G =4.5; cleavage, perfect; sometimes in flat crystals grouped so as to show wedge-like edges; color, white. Barite
H=3 to 3.5; G=4; cleavage, perfect; often fibrous; color, white, faintly blue. Celestite
H=3.5; G=3.7; cleavage, perfect; color, white. Strontianite
H=3.5; G=4.3; cleavage, distinct; color, white. Witherite
H=3.5; G=3.8; cleavage, perfect; color, white or gray, often rusty. Siderite
H=4.5; G=6; cleavage, distinct; color white or light brown or yellow. Scheelite
H=5; G=5; in roundish grains; color, red or brown. Monazite
H=5; G=4.3; mostly in roundish masses, crusts, etc., like calamine. Smithsonite
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