Scoria

Scoria is a type of igneous rock. Igneous rocks are rocks which solidify from molten material (i.e. magma). When magma cools, it can occur in two places - beneath the surface of the earth (plutonic) or on top of the surface (volcanic). Igneous rocks can be identified by the determination of the composition and texture of the rock.

The composition of scoria is mafic and its texture is vesicular. Mafic describes any silicate mineral or rock that is rich in magnesium and iron. The term is actually a portmanteau of the words "magnesium" and "ferric." Most mafic minerals and rocks are dark in color and have a relative density greater than 3. Vesicular texture denotes any volcanic rock characterized by having many cavities (known as vesicles) at its surface and inside. The vesicles form during the extrusion of magma to the surface. At the pressure decreases, magmatic gases are able to come out of the solution, forming gas bubbles in the magma. When the magma is extruded as lava and cools, the lava solidifies around the gas bubbles, preserving them as vesicles.

Interesting fact: The landscaping product commonly called "lava rock" is scoria

Another interesting fact: The cinder mix widely used on outdoor running tracks is made of scoria.

Other rocks that look similar to scoria are slag and pumice.

Sunset Crater in Arizona

Sunset Crater is one of the youngest scoria cones in the contiguous United States. It came about sometime between 1040 and 1100 A.D.

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

Types of Maps

Isarithmic Map

Isarithmic maps, also known as contour maps, depict smooth continuous phenomena such as rainfall, temperature, or population.

Above is an example of an isarithmic map showing the temperatures across the contiguous United States on August 9, 2000.

Choropleth Map

Choropleth Maps show statistical data aggregated over predefined regions, such as a state or country, using different colors or shadings of the same color.

Above is an example of a choropleth map depicting the estimated median household income across the contiguous United States in the year 2008. The darker shades represent the higher incomes.

Dot Density Map
Dot Density maps use the dot symbol (.) to show the presence of a particular feature or phenomena. They are useful for understanding global distributions of the mapped phenomena and comparing the relative densities of the different regions of the map.

Above is an example of a Dot Density map depicting the United States population distribution in the year 2000. For this particular map, one dot represents 7500 people.

Proportional Symbol Map

A Proportional Symbol map uses symbols of different sizes to represent data associated with the different areas on the map.

Above is an example of a Dot Density map depicting the number of Walmart stores per state in the United States in 2009. The larger the dot the larger the quantity of Walmart stores in that particular state.

My Isarithmic  Map of Annual Precipitation in Georgia

As can be seen with the legend, the darker the shade of blue, the greater the amount of precipitation.