An Assortment of Rocks

Amethyst

Amethyst is commonly found in jewelry

Info about Amethyst:

Color: purple / violet

Crystal Habit: 6-sided prism ending in 6-sided pyramid

Crystal System: rhombohedral class 32

Cleavage: none

Fracture: conchoidal

Mohs Scale Hardness: 7

Luster: glossy

Streak: white

Diaphaneity: transparent to translucent

Specific Gravity: 2.65 constant

Melting Point: 1650 degrees Celsius

Solubility: insoluble in common solvents

Feldspar

Info about Feldspar:

Color: pink, white, gray, brown

Crystal System: triclinic or monoclinic

Cleavage: two or three

Fracture: along cleavage planes

Mohn Scale Hardness: 6

Luster: vitreous

Streak: white

Diaphaneity: opaque

Specific Gravity: 2.55-2.76

Galena

Info about Galena:

Color: lead gray and silvery

Crystal Habit: cubes and octahedra, tabular, and sometimes skeletal crystals

Crystal System: hexoctahedral

Cleavage: cubic

Fracture: subconchoidal

Tenacity: brittle

Mohs Scale Hardness: 2.5-2.75

Luster: metallic

Streak: lead gray

Diaphaneity: opaque

Specific Gravity: 7.2-7.6

Quartz

Info about Quartz:

Color: colorless to black, through various colors

Crystal Habit: six-sided prism ending in six-sided pyramid

Crystal System: trigonal trapezohedral, hexagonal

Cleavage: indistinct

Fracture: conchoidal

Tenacity: brittle

Mohs Scale Hardness: 7

Luster: vitreous - waxy to dull when massive

Streak: white

Diaphaneity: transparent to nearly opaque

Specific Gravity: 2.65

Melting Point: 1670 degrees Celsius

Solubility: insoluble at STP

Halite

Info about Halite:

Color: colorless or white; also blue, purple, red, pink, yellow, orange, or gray

Crystal Habit: predominantly cubes

Crystal System: cubic

Cleavage: perfect; three directions cubic

Fracture: conchoidal

Tenacity: brittle

Mohs Scale Hardness: 2-2.5

Luster: vitreous

Streak: white

Diaphaneity: transparent

Specific Gravity: 2.17

Solubility: water soluble

Calcite

Info about Calcite:

Color: colorless or white; also gray, yellow, green

Crystal Habit: crystalline, granular, stalactitic, concretionary, massive, rhombohedral

Crystal System: trigonal hexagonal scalenohedral

Cleavage: perfect on three directions

Fracture: conchoidal

Tenacity: brittle

Mohs Scale Hardness: 3

Luster: vitreous to pearly

Streak: white

Diaphaneity: transparent to translucent

Specific Gravity: 2.71

Solubility: soluble in dilute acids