Glossary

  • Abbot Richard (1720(?) - about 1800; real name — Jerome Richard) — an 18th century French writer, travelled in Italy, returned to France around 1766, settled in Paris.

  • Agostino del Riccio (1541-1598) — a Dominican monk and the author of The History of Stones, a detailed description of the many minerals that Riccio came across in the Grand Duke's Workshop where he learned to work with stone. He also wrote several volumes on agriculture. He spent his last years in the Basilica of Santa Maria Novella as curator of the monastery gardens.

  • Amphibole — a group of inosilicate minerals of complex variable composition, the basis of the structure of which are chains of silicon-oxygen tetrahedrons. The general formula of amphiboles is AB2C5T8O22W2. The chemical composition is divided into calcium (actinolite, tremolite), sodium (riebeckite, arfvedsonite), lithium and mixed subgroups. Its hardness on the Mohs scale is 5.5-6.

  • Aragonite — an unstable phase of calcium carbonate CaCO3, whose crystalline structure changes to calcite over 10-100 million years. Aragonite is part of the nacreous shell layer of many species of shellfish, and the exoskeleton of corals. Aragonite forms the thinnest layers of pearls.

  • Archetto — a small saw made from a bent chestnut rod and stretched iron wire. It looks like an arch - hence the name. It is traditionally used for precise sawing of shaped elements from a thin cut of stone when making commesso di pietre dure. During the work, the master adds an abrasive moist material to the wire with every movement, allowing delicate sawing of both hard and soft stones. All these nuances help avoid unnecessary cracks and damage to expensive material.

  • Calcite — calcium carbonate CaCO3, one of the most widespread minerals on Earth, in particular it is rock-forming (it is a monocomponent of metamorphic rocks - marble, sedimentary limestone and organogenic sedimentary mineral - chalk). It forms crystals and crystalline aggregates up to criptoccrystalline with crystalline size up to 0.01 mm. Its hardness on the Mohs scale is 3, cleavage is perfect in three directions.

  • The Casino Mediceo di San Marco — a Late Renaissance palazzo in Florence, built on the site of the workshops and Academy of Arts (Accademia degli Orti Medicei) that had been there since Lorenzo Medici the Magnificent (1449-1492). In 1494, the Medici were expelled from the city and the workshops gradually declined. Thanks to Francesco I Medici (1541-1587), the artistic centre was revived and reconstructed in 1568-1574: various workshops and laboratories, including alchemical ones, were set up here.

  • Cleavage — the ability of crystals and crystal grains to split in specific crystallographic directions.

  • Commesso di pietre dure (literally "combination of hard stones") — a mosaic set of hard stones, which include ornamental and semiprecious stones. It is considered the most used international term for "Florentine mosaic".

  • Dolomite — calcium magnesium carbonate CaMg(CO3)2. It makes up95% of the sedimentary rock of the same name and modified (dolomized) limestones. Named after the French mineralogist and geologist Deod de Dolomieu, it was discovered as a separate mineral species in the Alps (area of the modern Dolomite Alps). Its hardness is 3.5-4 on the Mohs scale, and its cleavage is perfect in one direction.

  • Ferdinando I Medici (1549-1609) — Grand Duke of Tuscany from 1587 to 1609. He was the patron of the arts.

  • Garnet (group) — silicate minerals with general formula R32+R23+[SiO4]3. Due to high hardness (6,5-7,5 on Mohs scale) and imperfect cleavage crystals of transparent garnet are widely used in decorative art from ancient times up to the present. Among the group the most notable ones are: almandine Fe 32+Al2[SiO4]3, pyrope Mg3Al2[SiO4]3, glossular Ca3Al2[SiO4]3, andraditis (demantoid) Ca3Fe23+[SiO4]3, uvarovite Ca3Cr2[SiO4]3.

  • Geode — a geological formation, a closed cavity in sedimentary or some volcanic rocks, partially or almost entirely filled with cryptocrystalline or phanerocrystalline aggregates of mineral crystals.

  • The Grand Duke's Workshop Galleria dei Lavori as a group of joint workshops under the patronage of the Grand Duke of Tuscany Francesco I Medici (1541-1587) dates back to 1580 (located at the Casino di San Marco in Florence). However, the official date is September 3, 1588, when Ferdinando I de' Medici (1549-1609) reorganized the workshops that were already in the Uffizi Palace at that time. The Medici contributed to the development of various fine arts, inviting the best not only Italian but also Northern European craftsmen to work there. In 1796 the workshops moved, and by the end of the 19th century they had completely changed their main field of work, becoming a major restoration centre that still functions today and is called the Opificio delle Pietre Dure (Hardstone Workshop).

  • Gypsum — calcium sulfate CaSO4х2H2O, its type - alabaster - is a homogeneous cryptocrystalline and dense material used for stone-cutting. Its hardness on the Mohs scale is 2.

  • Hydrothermal processes — endogenous geological processes of formation and transformation of minerals and ores occurring in the Earth's crust at medium and shallow depths with participation of hot water solutions at high pressures.

  • Jacopo Ligozzi (1547-1627) — an Italian artist and miniaturist. After his death in 1574, Giorgio Vasari headed the Florentine Academy of Drawing. Some of Ligozzi's finest works are virtuoso drawings of flora and fauna, thanks to which, among other things, he was invited to work at the court of the Medici.

  • Jade — an interwoven-fibrous cryptocrystalline aggregate of the silicate mineral of the actinolith-tremolite group - amphibole of Ca2(Mg,Fe)5[Si8O22](OH)2 composition. The hardness of the mineral is low - 5.5-6 on the Mohs scale, but its impact toughness is extremely high: jade is difficult to split. Due to this property, jade is used as an ornamental and even high jewelry material.

  • Jasper — a dense cryptocrystaline rock composed mainly of quartz, chalcedony and pigmented admixtures of other minerals (epidote, actinolite, chlorite, mica, pyrite, oxides and hydrooxides of iron and manganese). It is a semi-precious ornamental stone. It is usually of sedimentary (sometimes volcanogenic) origin. Its hardness on the Mohs scale is 7. By the nature of the pattern jasper is divided into brecciated, spotted, striped, agate and other types. Often they are named after the place of extraction.

  • Limestone — a sedimentary, detrital rock of organic, less often of chemogenic origin, consisting mainly of calcium carbonate (CaCO3) in the form of calcite crystals of various sizes. Coral limestone is a hard porous limestone rock composing coral reefs. It consists mainly of the skeletons of coral colonies with an admixture of shells of clams and foraminifera, shells of echinoderms.

  • Listvenite — a rock of metamorphic origin consisting of quartz, carbonates and mica (fuccite).

  • Louis XIV (1638-1715) — King of France from 1643 to 1715. His reign was the longest in the history of Europe. Patron of the arts. Under his reign at the Gobelins Manufactory mosaics from semiprecious stones - commesso di pietre dure - were produced. Based on popular compositions of the Florentine Workshop of the Grand Duke, masters of the manufactory were able to create their own recognizable style.

  • Lyapis-lazuli — complex aluminosilicate-sulphate of sodium Na[(AlSiO4)SO4]. On the Mohs scale it is classified as a semihard stone (5.5). It is rarely found in the form of crystals, more often in the form of massive specimen in which minerals are fused with lazurite: sodalite a8[AlSiO4]6Cl2, calcite CaCO3 and pyrite FeS2. The name "lazurite" appeared only in the 18th century. The pigment, which was obtained by grinding the mineral into powder, was used in painting and was the most expensive - its color saturation does not fade with time. It has numerous names, including "Bukhara stone".

  • Marble (Ancient Greek μάρμαροσ — "white or shiny stone")  — a metamorphic rock consisting only of CaCO3 calcite. When dolomite CaMg(CO3)2 is recrystallized, dolomite marbles are formed. Its hardness on the Mohs scale is 2.5-3.5. Depending on the admixture of other minerals, the marble has various decorative qualities. It is often called by the name of the place of extraction.

  • Marble onyx and aragonite onyx — a dense, often striped aggregate of calcite minerals or, less frequently, aragonite.

  • Metamorphism (Ancient Greek μετα-μορφόομαι — "I transform") — the process of hard phase mineral and structural change of rocks under the influence of temperature and pressure in the presence of a fluid - any solvent or gas.

  • Minerals — homogeneous natural chemical compounds, which are or were in crystalline state. They are a component of rocks, ores and meteorites.

  • Modello — preparatory work, demonstrating the master's idea for an artwork. It can be an oil or pencil sketch on paper or a canvas, or a small three-dimensional model made of plaster or clay for a sculpture or architectural form.

  • The Mohs scale — a classification of minerals by hardness, created by the German scientist Friedrich Mohs (1773-1839) in 1833. The scale is divided into 10 degrees, including internal gradation into soft, semi-hard and hard stones. Hard minerals with an index from 6 to 10: orthoclase, quartz, topaz, corundum, diamond.

  • Naturalia — object or material of exclusively natural origin. The term is usually applied to objects in a natural science collection.

  • Obsidian — a magmatic rock, a kind of volcanic glass, often corresponding to granite in composition. Uncrystallised volcanic glass, unlike minerals, has no crystalline structure, but its fragments may contain quartz crystals. Its hardness on the Mohs scale is 6.5-7.

  • Opal — an amorphous silicon dioxide SiO2. Instead of the crystal structure, opal has a closest packing periodic arrangement of silica globules (rounded particles).

  • Оpus sectile (lat. — "sectile work") — stone mosaic technique, considered the original source of commesso di pietre dure. It appeared about the 3rd century B.C. and was popular in Ancient and Medieval Rome. Unlike the Roman mosaic opus tesselatum, which used identically shaped small square elements - tessers, for opus sectile parts of different shapes are used.

  • Pietre dure (literally "hard stones" — minerals which have a Mohs scale index above 6) — a term referring to the technique of working with semi-precious and ornamental stones, which was used to manufacture both flat mosaics and three-dimensional objects (vases, small statuary, etc.).

  • Pietre tenere (literally "soft stones") — minerals which have a Mohs scale index from 1 to 5 inclusive. Of these, marble, breccia, alabaster and limestone are often used in mosaics.

  • Quartz — silicon dioxide SiO2, the second most common mineral on Earth. It is a rock-forming monomineral in many types of rocks (jasper, quartzite) and formations (silicon, chalcedony, agate), where it is represented by microcrystalline aggregates. It forms crystals: from small to large and giant (up to 200-300 kg). Quartz in crystals of the size visible to the eye has varieties of color: rock crystal — colorless; amethyst — purple; citrine — yellow; smoky quartz, or rauchtopaz — gray; morion — black. Cryptocrystalline quartz aggregates, consisting of the smallest crystals and having homogeneous or striped structure, — chalcedonies and agates — also have names of color varieties: carnelian, sardonyx, or carneole are orange-red; plasma — green with red dots; chrysoprase — apple-green. Hardness of quartz on the Mohs scale is 7, cleavage is imperfect. The hardness of quartz aggregates (chalcedony and jasper) is lower — up to 6-6.5 — due to admixtures of other, softer minerals.

  • Rhodusitis is a collective term for stone-cutting material from grey turquoise to grey, consisting of a mixture of alkaline (sodium) amphiboles of riebeckite, arfvedsonite and others with quartz. Often this material, when properly processed, has the optical effect of a cat's eye and is called "hawk's-eye" and "pietersite". Chemical formula: NaNa2(Mg;Fe)4Fe(OH)2(Si4O11). Its hardness on the Mohs scale is 5.5-6.

  • Rocks are substances that compose the Earth's crust. They consist of homogeneous or heterogeneous minerals of various hardness.

  • Serpentine (group) — silicate minerals with general formula X2-3Si2O5[OH]4, where X = Mg, Fe, Ni, Al, Zn, Mn. Serpentines antigorite, chrysotile and lizardite are rock-forming and constitute the main volume of serpentinite rock, including the so-called green marble, an ornamental and facing stone of green color.

  • Serpentinite (green marble) — a green stone rock, which consists of minerals of serpentinite group and formed as a result of serpentinization under the influence of temperature and pressure of ultrabasic rocks or dolomites. As a rule, serpentinite contains inclusions of chromite mineral in the form of small black crystals (dots), which is the source of green color of the rock.

  • Serpentinization — a process of change (hydration) of ultrabasic rocks under the influence of thermal aqueous solutions, expressed in substitution of anhydrous magnesian silicates with serpentinite group minerals. Serpentinites are formed as a result of serpentinization.

  • Slate board — a plate, which is a compressed rock: clay-shale. Other names: slate, natural slate. It is known that already in the Middle Ages shale was widely used.

  • Verde dell’Arno (literally "green of the Arno river") — a mineral, which according to the Mohs scale belongs to semi-hard rocks. To this day, it is mined only at the mouth of the Arno River (in particular, it gives the river its greenish hue). It is considered to be a distinctive material for Tuscany — many objects were made of it there. It was supplied to other regions of Europe, but was used there less, as it was an expensive imported material.