Friday, February 17, 2012

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.


Wednesday, February 8, 2012

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

Wednesday, February 1, 2012

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.