igneous, sedimentary, and metamorphic
Author's Note
Before you read this, I must inform you that I read the whole Wikipedia page for rocks before I wrote this.
igneous, sedimentary, and metamorphic
Apple Bloom, Scootaloo, and Sweetie Belle bounced down the path to the gray rock farm happily.
"We're totally gonna get our cutie marks in rock science!" Scootaloo shouted enthusiastically to her friends,
Apple Bloom nodded and said with a smile, "Especially with the help o' Pinkie Pie's sister. Applejack says she knows a lotta stuff 'bout rocks."
Sweetie Belle's horn sparked light green from excitement, "I'm just so excited I could burst!"
They eventually arrived to the small house, where Pinkie Pie used to live.
Outside of the house was a gray pony with a light purple mane, she looked as if she had been turned to stone.
Apple Bloom grinned, "Heya Ms. Pie! Ya' gonna teach us 'bout rocks?"
Maud nodded, a small, weak smile crept onto her lips.
The Cutie Mark Crusaders sat down in front of Maud expectantly.
Maud picked up one of the rocks that were sitting around the dirt road, and began.
"Rocks come in all different kinds, often certain types of rocks, mostly ones in mines, have diamonds inside of them.
Sedimentary rocks are formed by the deposition of material at Equestria's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles, to settle and accumulate or minerals to precipitate from a solution. Particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, sediment was formed by weathering and erosion in a source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers which are called agents of denudation."
The Cutie Mark Crusaders watched in awe as Maud explained the history of Sedimentary rocks,
"The sedimentary rock cover of the continents of Equestria's crust is extensive, but the total contribution of sedimentary rocks is estimated to be only 8% of the total volume of the crust. Sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding. The study of sedimentary rocks and rock strata provides information about the subsurface that is useful for civil engineering, for example in the construction of roads, houses, tunnels, canals or other constructions. Sedimentary rocks are also important sources of natural resources like coal, fossil fuels, drinking water or ores.
"Moving onto Metamorphic rocks," Maud said, then picked up a rock that was to the left of her,
"Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock is subjected to heat and pressure causing profound physical and/or chemical change. The protolith may be sedimentary rock, igneous rock or another older metamorphic rock.
"Metamorphic rocks make up a large part of Equestria's crust and are classified by texture and by chemical and mineral assemblage They may be formed simply by being deep beneath Equestria's surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion. They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's interior. The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides information about the temperatures and pressures that occur at great depths within the Earth's crust. Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite."
Sweetie Belle was now levitating a note pad and pen, taking notes and listening intensely.
"Now to the last most common type of rock, Igneous rocks.
"Igneous rock (derived from the Latin word ignis meaning fire) is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Over 700 types of igneous rocks have been described, most of them having formed beneath the surface of Equestria's crust."
The three fillies' eyes were wide with excitement, Maud was about to go on about rock classification until Scootaloo interrupted her,
"Maud, how do you know all this about rocks?"
Maud's weak smile began to grow into a grin, "I grew up on a rock farm." She said in her usual dead-pan tone.
Sweetie Belle set down her note pad, "Stop yapping! We have cutie marks to earn!" She said, her voice cracked.
Maud's smile faded back into the weak smile, then she said,
"At a granular level, rocks are composed of grains of minerals, which, in turn, are homogeneous solids formed from a chemical compound that is arranged in an orderly manner. The aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed. Many rocks contain silica, a compound of silicon and oxygen that forms 74.3% of Equestria's crust. This material forms crystals with other compounds in the rock. The proportion of silica in rocks and minerals is a major factor in determining their name and properties.
"Rocks are geologically classified according to characteristics such as mineral and chemical composition, permeability, the texture of the constituent particles, and particle size. These physical properties are the end result of the processes that formed the rocks. Over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock: igneous, sedimentary, and metamorphic.
The three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks. By increase or decrease in the proportions of their constituent minerals they pass by every gradation into one another, the distinctive structures also of one kind of rock may often be traced gradually merging into those of another. Hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series."
Scootaloo yawned, "It's getting late, guys."
Apple Bloom shook her head, "Yeah. Mind if this be the end of today's lesson, Ms. Pie?"
Maud shook her head, then looked in front of her at a rock, then nudged it with her nose towards the three fillies,
"Take it. It's a igneous rock."
The three smiled, then Sweetie Belle picked up the rock with her magic.
"Thank you, Maud!" They all called out as they walked back to Ponyville.
