Ogg Superfamily
Inspired by the hand lettering of 20th century book designer and calligrapher Oscar Ogg, Ogg captures the unique mix of calligraphic and typographic form achieved through his use of hand carved pen nibs, brushes, and white-out. The transitional stroke ductus of Ogg roman made for maximum legibility with an extremely compact word-shape, even when set at 8pt and below. In this vein, Ogg Text came to take on an unmistakably Dutch flavor.
Like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera. These organisms secrete shells made of aragonite or calcite, and leave these shells behind when they die. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and extraclasts. Limestone often contains variable amounts of silica in the form of chert (chalcedony, flint, jasper). Limestone has numerous uses: as a building material, an essential component of concrete (Portland cement), as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feedstock for the production of lime, as a soil conditioner, or as a popular decorative addition to rock gardens. The primary source of the calcite in limestone is most commonly marine organisms. Some of these organisms can construct mounds of rock known as reefs, building upon past generations. Limestone has numerous uses: as a building material, an essential component of concrete (Portland cement), as aggregate for the base of roads, as a chemical feedstock for the production of lime, as a soil conditioner, and for rock gardens.
Some limestones do not consist of grains at all, and are formed completely by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems, such as stalagmites and stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular (oolite) appearance. The primary source of the calcite in limestone is most commonly marine organisms. Some of these organisms can construct mounds of rock known as reefs, building upon past generations. Limestone has numerous uses: as a building material, an essential component of concrete (Portland cement), as aggregate for the base of roads, as a chemical feedstock for the production of lime, as a soil conditioner, and for rock gardens. The primary source of the calcite in limestone is most commonly marine organisms. Some of these organisms can construct mounds of rock known as reefs, building upon past generations. Limestone has numerous uses: as a building material, an essential component of concrete (Portland cement), as aggregate for the base of roads, as a chemical feedstock for the production of lime, as a soil conditioner, and for rock gardens.
In the US, aragonite in the form of stalactites and “cave flowers” is known from Carlsbad Caverns and other caves. Massive deposits of oolitic aragonite sand are found on the seabed in the Bahamas. ragonite is the high pressure polymorph of calcium carbonate. As such, it occurs in high pressure metamorphic rocks such as those formed at subduction zones. Aragonite forms naturally in almost all mollusk shells. The type location for aragonite is Molina de Aragón in the Province of Guadalajara in Castilla-La Mancha, Spain, for which it was named in 1797. The mineral is not named for the region of Aragon: Molina de Aragón is located in the historic region of Castile. Turquoise is insoluble in all but heated hydrochloric acid. Its streak is a pale bluish white and its fracture is conchoidal, leaving a waxy lustre. Despite its low hardness relative to other gems, turquoise takes a good polish. Turquoise may also be peppered with flecks of pyrite or interspersed with dark, spidery limonite veining.
Aragonite also forms in the ocean and in caves as inorganic precipitates called marine cements and speleothems, respectively. Aragonite is not uncommon in serpentinites where high Mg in pore solutions apparently inhibits calcite growth and promotes aragonite precipitation. Aragonite is metastable at the low pressures near the Earth’s surface and is thus commonly replaced by calcite in fossils. Aragonite older than the Carboniferous is essentially unknown. It can also be synthesized by adding a calcium chloride solution to a sodium carbonate solution. As a secondary mineral, turquoise forms by the action of percolating acidic aqueous solutions during the weathering and oxidation of preexisting minerals. For example, the copper may come from primary copper sulfides such as chalcopyrite or from the secondary carbonates malachite or azurite; the aluminium may derive from feldspar; and the phosphorus from apatite. Climate factors appear to play an important role as turquoise is typically found in arid regions, filling or encrusting cavities and fractures in typically highly altered volcanic rocks, often with associated limonite and other iron oxides.
In aquaria, aragonite is considered essential for the replication of reef conditions. Aragonite provides the materials necessary for much sea life and also keeps the pH of the water close to its natural level, to prevent the dissolution of biogenic calcium carbonate. Aragonite has been successfully tested for the removal of pollutants like zinc, cobalt and lead from contaminated wastewaters. Aragonite is thermodynamically unstable at standard temperature and pressure, and tends to alter to calcite on scales of 107 to 108 years. The mineral vaterite, also known as μ-CaCO3, is another phase of calcium carbonate that is metastable at ambient conditions typical of Earth’s surface, and decomposes even more readily than aragonite. For example, the copper may come from primary copper sulfides such as chalcopyrite or from the secondary carbonates malachite or azurite; the aluminium may derive from feldspar; and the phosphorus from apatite. Climate factors appear to play an important role as turquoise is typically found in arid regions, filling or encrusting cavities and fractures in typically highly altered volcanic rocks, often with associated limonite and other iron oxides.