Chalk
Chalk /ˈtʃɔːk/ is a soft, white, porous sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite shells (coccoliths) shed from micro-organisms called coccolithophores. Flint (a type of chert unique to chalk) is very common as bands parallel to the bedding or as nodules embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified (i.e. replaced molecule by molecule by flint).
Chalk as seen in Cretaceous deposits of Western Europe is unusual among sedimentary limestones in the thickness of the beds. Most cliffs of chalk have very few obvious bedding planes unlike most thick sequences of limestone such as the Carboniferous Limestone or the Jurassic oolitic limestones. This presumably indicates very stable conditions over tens of millions of years.
Chalk (disambiguation)
Chalk may refer to:
Surname
Magnesium carbonate
Magnesium carbonate, MgCO3 (archaic name magnesia alba), is an inorganic salt that is a white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals.
Forms
The most common magnesium carbonate forms are the anhydrous salt called magnesite (MgCO3) and the di, tri, and pentahydrates known as barringtonite (MgCO3·2 H2O), nesquehonite (MgCO3·3 H2O), and lansfordite (MgCO3·5 H2O), respectively. Some basic forms such as artinite (MgCO3·Mg(OH)2·3 H2O), hydromagnesite (4 MgCO3·Mg(OH)2·4 H2O), and dypingite (4 MgCO3· Mg(OH)2·5 H2O) also occur as minerals.
Magnesite consists of white trigonal crystals. The anhydrous salt is practically insoluble in water, acetone, and ammonia. All forms of magnesium carbonate react in acids. Magnesium carbonate crystallizes in the calcite structure where in Mg2+ is surrounded by six oxygen atoms. The dihydrate one has a triclinic structure, while the trihydrate has a monoclinic structure.
References to 'light' and 'heavy' magnesium carbonates actually refer to the magnesium hydroxy carbonates hydromagnesite and dypingite (respectively).
Bank
A bank is a financial institution that creates credit by lending money to a borrower, thereby creating a corresponding deposit on the bank's balance sheet. Lending activities can be performed either directly or indirectly through capital markets. Due to their importance in the financial system and influence on national economies, banks are highly regulated in most countries. Most nations have institutionalized a system known as fractional reserve banking under which banks hold liquid assets equal to only a portion of their current liabilities. In addition to other regulations intended to ensure liquidity, banks are generally subject to minimum capital requirements based on an international set of capital standards, known as the Basel Accords.
Banking in its modern sense evolved in the 14th century in the rich cities of Renaissance Italy but in many ways was a continuation of ideas and concepts of credit and lending that had their roots in the ancient world. In the history of banking, a number of banking dynasties — notably, the Medicis, the Fuggers, the Welsers, the Berenbergs and the Rothschilds — have played a central role over many centuries. The oldest existing retail bank is Monte dei Paschi di Siena, while the oldest existing merchant bank is Berenberg Bank.
Rampart (fortification)
A rampart in fortification architecture is a length of bank or wall forming part of the defensive boundary of a castle, hillfort, settlement or other fortified site. It is usually broad-topped and made of excavated earth or masonry or a combination of the two.
Early fortifications
Many types of early fortification, from prehistory through to the Early Middle Ages, employed earth ramparts usually in combination with external ditches to defend the outer perimeter of a fortified site or settlement.Hillforts, ringforts or "raths" and ringworks all made use of ditch and rampart defences, and of course they are the characteristic feature of circular ramparts. The ramparts could be reinforced and raised in height by the use of palisades. This type of arrangement was a feature of the motte and bailey castle of northern Europe in the early medieval period.
Types of rampart
The composition and design of ramparts varied from the simple mounds of earth and stone, known as dump ramparts, to more complex earth and timber defences (box ramparts and timberlaced ramparts), as well as ramparts with stone revetments. One particular type, common in Central Europe, used earth, stone and timber posts to form a Pfostenschlitzmauer or "post-slot wall". Vitrified ramparts were composed of stone that was subsequently fired, possibly to increase its strength.
Bank (card game)
Bank, also known also as "Polish Bank" or "Russian Bank," is the name of a comparing card game. The game requires a standard 52-card deck and five or six players.
Rules
At the start of the game, each player contributes an arranged stake to the pool. The dealer gives three cards to each player and turns up another; if this is not lower than an eight (ace is lowest), the dealer continues turning up cards until such a card is exposed. The player on the dealer's left, without touching or looking at the three cards received, can bet the amount of the pool, or any part of it, that among those cards is one that is higher (of the same suit) than the turn-up. If the player wins, the player takes the amount from the pool; if the player loses, the player pays that amount to the pool. Each player does the same in turn, the dealer last. Whenever the pool is exhausted, a fresh stake is put into the pool. After a round is over the deal passes. No player may touch any cards received until making a bet; the penalty is a fine to the pool of twice the stake, and the loss of the right to bet during that round.
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