Throughout the Black Rock area in Nevada one finds every conceivable rock you can think of.  Just about all of us have no idea what we are looking at.  Our rock collecting is picking up "monkey rocks', those shiny or neat looking peices everywhere.  In reality we come across all sorts of interesting things we actually take for granite -granted. This glossary defines many of the rocks we find with accurate descriptions and sometimes photos. Most of these rocks have crystal formations associated with them; which we do not cover. It is not intended to be a Geology Lesson.

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PERLITE - is an amorphous volcanic glass that has relatively high water content, typically formed by the hydration of obsidian. Perlite has the unusual characteristic of expanding and becoming porous when it is heated. It can expand to as much as twenty times its original volume. Expansion occurs when the glassy lava rock is heated to 1600 degrees F (871 degrees C) and the water molecules trapped in the rock turn into vapor causing the rock to expand. (This is the same principle as the water in popcorn that causes the kernel to pop when it is heated.) Before it is expanded, Perlite is commonly gray, but can also be green, brown, blue or red. After it has been heated, perlite is typically light gray to white
PETRIFIED WOOD - is the name given to a special type of fossilized remains of terrestrial vegetation. It is the result of a tree or tree-like plants having completely transitioned to stone by the process of permineralization. All the organic materials have been replaced with minerals (mostly a silicate, such as quartz), while retaining the original structure of the stem tissue. Elements such as manganese, iron, and copper in the water/mud during the petrification process give petrified wood a variety of color ranges. Pure quartz crystals are colorless, but when contaminants are added to the process the crystals take on a yellow, red, or other tint. Unlike other types of fossils which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material. The petrifaction process occurs underground, when wood becomes buried under sediment or volcanic ash and is initially preserved due to a lack of oxygen which inhibits aerobic decomposition. Mineral-laden water flowing through the covering material deposits minerals in the plant's cells; as the plant's lignin and cellulose decay, a stone mold forms in its place. The organic matter needs to become petrified before it decomposes completely.
PLUTONS - In geology, a pluton is a body of intrusive igneous rock (called a plutonic rock) that is crystallized from magma slowly cooling below the surface of the Earth. Plutons include batholiths, stocks, dikes, sills, laccoliths, lopoliths, and other igneous bodies. In practice, "pluton" usually refers to a distinctive mass of igneous rock, typically several kilometers in dimension, without a tabular shape. Batholiths commonly are aggregations of plutons. The most common rock types in plutons are granite, granodiorite, tonalite, monzonite, and quartz diorite. Generally light colored, coarse-grained plutons of these compositions are referred to as granitoids..
PYRRHOTITE - A russet colored iron sulfide mineral. It is also called magnetic pyrite, because the color is similar to pyrite and it is weakly magnetic. The magnetism decreases as the iron content increase. Pyrrhotite is a rather common trace constituent of mafic igneous rocks especially norites. It occurs as segregation deposits in layered intrusions associated with pentlandite, chalcopyrite and other sulfides. It occurs in masses associated with copper and nickel mineralisation. It also occurs in pegmatites and in contact metamorphic zones. Pyrrhotite is often accompanied by pyrite, marcasite and magnetite. Pyrrhotite does not have specific applications. It is mined primarily because it is associated with pentlandite, sulfide mineral that can contain significant amounts of nickel and cobalt.
PYRITE - or iron pyrite, also known as fool's gold, is an iron sulfide. This mineral's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold. The color has also led to the nicknames brass, brazzle, and Brazil, primarily used to refer to pyrite found in coal. Pyrite is the most common of the sulfide minerals. In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel. Pyrite is usually found associated with other sulfides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds and as a replacement mineral in fossils. Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold. Gold and arsenic occur as a coupled substitution in the pyrite structure.
QUARTZ - is the second-most-abundant mineral in Earth's continental crust, after feldspar. Its crystal structure is a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucentl. Common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. Quartz is a defining constituent of granite and other felsic igneous rocks. It is very common in sedimentary rocks such as sandstone and shale and is also present in variable amounts as an accessory mineral in most carbonate rocks. It is a common constituent of schist, gneiss, quartzite and other metamorphic rocks. Quartz has the lowest potential for weathering and consequently it is very common as a residual mineral in stream sediments and residual soils. While the majority of quartz crystallizes from molten magma, much quartz also chemically precipitates from hot hydrothermal veins, sometimes with ore minerals like gold, silver and copper. Large crystals of quartz are found in magmatic pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms.

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