Turquoise
Turquoise has been used for jewelry and decoration for thousands of years. The turquoise on the right is typical turquoise, while the sample on the left has had the copper replaced by iron. Iron can also cause yellow turquoise. Turquoise is usually altered to improve either its color or hardness, as it is a porous mineral and easy to alter. Unaltered turquoise is hard to find.
Color: Sky-blue, blue-green, apple-green
Color of streak: White
Moh’s hardness: 5-6
Density: 2.31-2.84 grams/cubic centimeter
Cleavage: None
Fracture: Conchoidal, uneven
Crystal system: (Triclinic) seldom; grape-shaped aggregates
Chemical composition: CuAl6(PO4)4(OH)8•5(H2O); a copper containing basic aluminum phosphate
Transparency: Translucent, opaque
Refractive index: 1.610-1.650
Double refraction: +0.040
Dispersion: None
Pleochroism: Absent
Absorption spectrum: (460), 432, (422)
Fluorescence: Week, green-yellow, light blue
Sulfur
One of the most commonly known attributes of sulfur is its smell. Its infamous aroma is caused a reaction between the sulfur and water, creating hydrogen sulfide (H2S). Its most common use is the production of sulfuric acid but it is also used in fertilizers and other agricultural products, gunpowder, matches, detergents and preservatives for wine and dried fruit.
Sulfur found naturally is written chemically as S8 as this allotrope of sulfur is most stable.
Sulfur is the tenth most abundant element in the universe.
The speckles in the upper right hand corner of the picture are small fragments of the sulfur. When I placed the samples on my scanner, the sulfur crumbled. You can see the results in the image.
Color: Bright yellow
Color of streak: Yellow
Moh’s hardness: 2
Density: 2.07 grams/cubic centimeter
Cleavage: Very poor in two directions
Fracture: Conchoidal
Crystal system: Orthorhombic
Chemical composition: S8 (Sulfur)
Transparency: Transparent to translucent
Refractive index: None
Double refraction: None
Dispersion: Unknown
Pleochroism: Unknown
Absorption spectrum: Unknown
Fluorescence: Unknown
Purity: >95%
Sodalite
Sodalite is a rare mineral. Hackmanite is an important variety of sodalite exhibiting tenebrescence. Originally discovered in 1806, it was not until vast deposits of good grade sodalite were found in Ontario that it became popular. It is used for ornamental objects, such as cabochons, beads and carved animals.
Color: White, blue and grey
Color of streak: White
Moh’s hardness: 5½-6
Density: 2.14-2.40
Cleavage: Indistinct
Fracture: Uneven, conchoidal
Crystal system: (Cubic) rhombic dodecahedra
Chemical composition: (Na4Al3(SiO4)3Cl) Sodium aluminium silicate with chlorine
Transparency: Transparent to opaque
Refractive index: 1.48
Double refraction: None
Dispersion: .018 (.009)
Pleochroism: Absent
Absorption spectrum: Not diagnostic
Fluorescence: Strong orange
Rock Crystal
Rock crystal is the official name given to what most people call quartz (”Quartz” covers a large umbrella of different minerals. Varieties of quartz are distinguished only by differences in the individual crystals on a molecular level). It is the most common mineral on the planet, since most sand and other rocks are made of rock crystal.
One interesting thing about rock crystal is that it is piezoelectric. This feature gave rock crystal’s first commercial success as phonograph needles. It is most commonly used today in watches, internal clocks for computers and as frequency stabilizers for radio transmitters.
Color: Colorless
Color of streak: White
Moh’s hardness: 7
Density: 2.65 grams/cubic centimeter
Cleavage: None
Fracture: Conchoidal, very brittle
Crystal system: Hexagonal prisms
Chemical composition: SiO2, silicon dioxide
Transparency: Transparent
Refractive index: 1.544-1.553
Double refraction: +0.009
Dispersion: 0.013 (0.008)
Pleochroism: Absent
Absorption spectrum: None
Fluorescence: None
Rock crystal can be synthetic.
Pyrite
Pyrite is most commonly known as “Fool’s Gold”. Pyrite is a secondary source for sulfur. During WWII, deposits of iron pyrite were mined for its sulfur and iron. Pyrite could be used as an ore for iron, but hematite and magnetite are more economical to mine and therefore they are primary ores.
The brightly colored reds, blues and greens are an optical anomaly. They are not a characteristic of pyrite under normal viewing conditions.
Color: Brass-yellow, gray-yellow
Color of streak: Green-Black
Moh’s hardness: 6 to 6 1/2
Density: 5 to 5.2 grams/cubic centimeter
Cleavage: Indistinct
Fracture: Conchoidal, uneven, brittle
Crystal system: Cubic, pentagonal, dodecahedra, octahedral
Chemical composition: FeS2, iron sulfide
Transparency: Opaque
Refractive index: Cannot be determined
Double refraction: None
Dispersion: None
Pleochroism: Absent
Absorption spectrum: Not diagnostic
Fluorescence: None
Amethyst
Amethyst is the most valuable variant within the quartz family. The crystals are always anchored to a base. The base is usually agate. The purplish color of this sample of amethyst is caused by atomic impurities found inside the crystal. Geologists do not know what these impurities are, but manganese, iron and sulfur are likely culprits.
Amethyst can be found in geodes and alluvial deposits.
Color: Purple, violet, pale red-violet
Color of streak: White
Moh’s hardness: 7
Density: 2.65 grams/cubic centimeter
Cleavage: None
Fracture: Conchoidal, very brittle
Crystal system: Hexagonal prisoms
Chemical composition: SiO2, silicon dioxide
Transparency: Transparent
Refractive index: 1.544-1.553
Double refraction: +0.009
Dispersion: 0.013 (0.008)
Pleochroism: Weak, reddish-violet, gray-violet
Absorption spectrum: (550-520)
Fluorescence: Weak, bluish