Vein (geology)

In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved is usually due to hydrothermal circulation.

Veins are classically thought of as being the result of growth of crystals on the walls of planar fractures in rocks, with the crystal growth occurring normal to the walls of the cavity, and the crystal protruding into open space. This certainly is the method for the formation of some veins. However, it is rare in geology for significant open space to remain open in large volumes of rock, especially several kilometers below the surface. Thus, there are two main mechanisms considered likely for the formation of veins: open-space filling and crack-seal growth.

Open space filling

Open space filling is the hallmark of epithermal vein systems, such as a stockwork, in greisens or in certain skarn environments. For open space filling to take effect, the confining pressure is generally considered to be below 0.5 GPa, or less than 3-5 kilometers. Veins formed in this way may exhibit a colloform, agate-like habit, of sequential selvages of minerals which radiate out from nucleation points on the vein walls and appear to fill up the available open space. Often evidence of fluid boiling is present. Vugs, cavities and geodes are all examples of open-space filling phenomena in hydrothermal systems.

Quartz

Quartz is the second-most-abundant mineral in Earth's continental crust, after feldspar. Its crystal structure is a continuous framework of SiO₄silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO₂.

There are many different varieties of quartz, several of which are semi-precious gemstones. Since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Europe and the Middle East.

Etymology

The word "quartz" is derived from the German word "Quarz" and its Middle High German ancestor "twarc", which probably originated in Slavic, cf. Czech tvrdý ("hard"), Polish twardy ("hard"), Serbian and Croatian tvrd ("hard").

The Ancient Greeks referred to quartz as κρύσταλλος (krustallos) derived from the Ancient Greek κρύος (kruos) meaning "icy cold", because some philosophers (including Theophrastus) apparently believed the mineral to be a form of supercooled ice. Today, the term rock crystal is sometimes used as an alternative name for the purest form of quartz.

Quartz (graphics layer)

In Apple computer's OS X operating system, Quartz is the Quartz 2D and Quartz Compositor part of the Core Graphics framework. Quartz includes both a 2D renderer in Core Graphics and the composition engine that sends instructions to the graphics card. Because of this vertical nature, Quartz is often synonymous with Core Graphics.

In a general sense, Quartz or Quartz technologies can refer to almost every part of the Mac OS X graphics model from the rendering layer down to the compositor including Core Image and Core Video. Other Apple graphics technologies that use the "Quartz" prefix include:

Quartz 2D & Quartz Compositor

Quartz 2D is the primary two-dimensional (2D) text and graphics rendering library: It directly supports Aqua by displaying two-dimensional graphics to create the user interface, including on-the-fly rendering and anti-aliasing. Quartz can render text with sub-pixel precision; graphics are limited to more traditional anti-aliasing, which is the default mode of operation but can be turned off. In Mac OS X v10.4, Apple introduced Quartz 2D Extreme, which allows Quartz 2D to use supported GPUs for rendering. In Mac OS X 10.4, Quartz 2D Extreme is not enabled by default, because it may lead to video redraw issues or kernel panics. As of Mac OS X v10.5 Quartz 2D Extreme has been renamed to QuartzGL. However, it still remains disabled by default, as there are some situations where it can degrade performance, or experience visual glitches; it is a per-application setting which can be turned on if the developer wishes.

Crystal oscillator

A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a precise frequency. This frequency is commonly used to keep track of time, as in quartz wristwatches, to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers. The most common type of piezoelectric resonator used is the quartz crystal, so oscillator circuits incorporating them became known as crystal oscillators, but other piezoelectric materials including polycrystalline ceramics are used in similar circuits.

Quartz crystals are manufactured for frequencies from a few tens of kilohertz to hundreds of megahertz. More than two billion crystals are manufactured annually. Most are used for consumer devices such as wristwatches, clocks, radios, computers, and cellphones. Quartz crystals are also found inside test and measurement equipment, such as counters, signal generators, and oscilloscopes.

List of The Demonata characters

This is a list of characters found in Darren Shan's The Demonata, a series of books that follows protagonists Grubbs Grady, Dervish Grady, Kernel Fleck and Bec MacConn on their quest against Lord Loss and his demon minions.

"Grubbs" Grady

Grubitsch "Grubbs" Grady is one of the main characters in The Demonata series. He is the protagonist of Lord Loss, Slawter, Blood Beast, Demon Apocalypse, Wolf Island, and Hell's Heroes. Grubbs makes appearances in Death's Shadow and Dark Calling. In Blood Beast Grubbs is afflicted by lycanthropy.

Grady Family

Grubbs Grady's family has been cursed with lycanthropy for many generations before the start of the first book. Bartholomew Garadex, an ancestor of Grubbs', struck a deal with Lord Loss that if he could beat him at three concurrent games of chess, then Lord Loss would cure a member of the Grady family from the curse. The tournament carried on through the generations of the Garadex/Grady family.

Grady-MacGrigor Family Tree

The Demonata

The Demonata is a series of books by best selling author Darren Shan. It deals with the world of demons (as opposed to his other series, The Saga of Darren Shan, which involves vampires). The series is told by three different protagonists: Grubbs Grady, Kernel Fleck, and Bec MacConn, the last of whom is the first female protagonist in a Darren Shan book. The series contains ten books.

The Books

Released

Cover illustration copyright Melvyn Grant

Chronological Order

Veining (metallurgy)

In metallurgy a veining (or finning) is the occurrence of a sheet like casting defect, produced by molten metal penetration into a sand casting mould.

a defect on the surface of a casting appearing as fins, veins or wrinkles and associated with excessive thermal movement of the sand, especially core sand

Description

Veining occurs as 'vein' like projections from a casting, usually at right angles to the casting's surface; the phenonoma can occur in any alloy, and is commonly seen in ferrous or copper based castings.

Veining has been attributed to temperature differences at distance from the molten metal resulting in differential thermal expansion in the sand leading to strain in, and failure of the sand mould. Research has shown that a main cause of veining is thermal expansion of the silica sand in combination with reduction in sand volume above 573C (after the alpha to beta silica phase transformation) due to softening/sintering and/or melting of sand grains, which results in cracking/voids.