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GEOLOGY FOR CIVIL ENGINEERS
GROUP 2 BUCCAT, GABRIEL EMIL DE GUZMAN, CHARLES MICO MARTINEZ, CLARENCE MATABANG, BRYAN ORLANDA, MECAH ELLA SAURE, CHARISSE JOY VALETE, JHOE AIRA MARIE
CHAPTER 2: MINERALOGY
LESSON 1: ELEMENTARY KNOWLEDGE ON SYMMETRY OF
CRYSTALLOGRAPHIC SYSTEMS
The minerals that make up igneous rocks crystallize at a range of different temperatures. This explains why a cooling magma can have some crystals within it and yet remain predominantly liquid. The sequence in which minerals crystallize from a magma is known as the Bowen Reaction Series. Of the common silicate minerals, olivine normally crystallizes first, at between 1200° and 1300°C. As the temperature drops, and assuming that some silica remains in the magma, the olivine crystals react with some of the silica in the magma to form pyroxene. As long as there is silica remaining and the rate of cooling is slow, this process continues down the Discontinuous Reaction Series (Ferromagnesian Minerals) : olivine to pyroxene, pyroxene to amphibole, and amphibole to biotite. At about the point where pyroxene begins to crystallize, Continuous Reaction Series (Plagioclase Feldspar) also begins to crystallize. At that temperature, the plagioclase is calcium-rich (anorthite). As the temperature drops, and providing that there is sodium left in the magma, the plagioclase that forms is a more sodium-rich variety.
WHO WAS BOWEN, AND WHAT’S A REACTION SERIES? Norman Levi Bowen Born in Kingston, Ontario; studied geology at Queen’s University and MIT. Joined Carnegie Institution (1912) and conducted magma cooling research. Developed Bowen’s Reaction Series , explaining the order of mineral crystallization. Bowen’s Reaction Series - One of Bowen's major contributions was the Bowen Reaction Series , which remains fundamental in understanding igneous rock formation. The term reaction is crucial, as minerals transform rather than simply coexisting. Discontinuous Branch o Olivine is the first mineral to form at ~1300°C. o As temperature drops, olivine becomes unstable , while pyroxene becomes stable. o The reaction: Mg₂SiO₄ + SiO₂ →2MgSiO₃ (Olivine reacts with silica to form pyroxene.) Plagioclase Zoning o When cooling happens quickly , plagioclase crystals develop zoning. o The core is calcium-rich , while the outer layers are sodium-rich due to progressive cooling. o This zoning can be observed under a microscope , showing a gradient from calcium-rich (center) to sodium-rich (outer layers). Final Crystallization o If the magma is silica-rich , some silica remains at 750°–800°C.
Forms basalt and gabbro (dark- colored rocks).
- Intermediate Magma Moderate silica (55%–65% SiO₂). Balanced FeO, MgO, CaO, Na₂O, and K₂O. Forms andesite and diorite (gray- colored rocks).
- Felsic Magma High silica (65%– 75% SiO₂). Low FeO, MgO, and CaO (~5%). High Na₂O + K₂O (~10%). Forms granite and rhyolite (light- colored rocks)
LESSON 2: PHYSICAL PROPERTIES OF MINERALS
Minerals o Rocks are composed of minerals o Minerals are naturally occurring, solid, crystalline, stable at room temperature, and inorganic substances. o Nearly 5000 known mineral species , but most rocks form from a few common ones. Rock-Forming Minerals - the vast majority of rocks are formed from combinations of a few common minerals o Main minerals that make up most rocks. o Examples : Feldspars, quartz, amphiboles, micas, olivine, garnet, calcite, pyroxenes. Accessory Minerals – it is minerals occurring within a rock in small quantities o Found in small amounts but provide geological history and age of rocks. o Examples : Zircon, monazite, apatite, titanite, tourmaline, pyrite. Elements in Earth’s Crust 98% of Earth's crust is made of eight elements: o Oxygen, silicon, aluminium, iron, magnesium, calcium, sodium, potassium. Mineral Formation and Magma Composition Igneous mineral composition depends on magma chemistry. o Iron & magnesium-rich magma → Olivine and pyroxene (e.g., basalt). o Silica-rich magma → Feldspar and quartz (e.g., granite). Minerals form in chemically compatible rocks (e.g., andalusite (Al₂SiO₅) won't form in aluminium-poor quartzite ). PHYSICAL PROPERTIES OF MINERALS Some minerals are easy to identify, while others require a petrographic microscope or advanced analysis. Identification should be based on multiple criteria rather than a single property, and using a hand lens can greatly assist in the process. COLOUR
Acicular Habit Botryoidal Habit (Malachite) Cubic Habit (Pyrite) Fibrous Habit (Silimanite) Hexagonal Habit (Sapphire) Foliated Habit (Biotite)
Massive Habit (Realgar) Platy Habit (Wulfenite) Prismatic Habit HARDNESS Hardness is a measure of how resistant a mineral is to scratching. This physical property is controlled by the chemical composition and structure of the mineral. Hardness is commonly measured on the Mohs scale. This is defined by ten minerals, where each mineral can scratch those with a lower scale number. Diamond (hardness 10) can scratch everything below it on the Mohs scale, but cannot itself be scratched, whereas quartz (hardness 5) can scratch calcite (hardness 3) but not corundum (hardness 9). SCALE NUMBER INDICATOR MINERAL
COMMON OBJECTS
1 Talc Fingernail 2 Gypsum Fingernail 3 Calcite Copper Coin 4 Fluorite Steel Knife 5 Apatite Knife Blade 6 Orthoclase Window Glass 7 Quartz Steel File 8 Topaz scratch most metals 9 Corundum second hardest mineral 10 Diamond can scratch all materials STREAK The streak of a mineral refers to the colour of the mark it leaves behind after being rubbed against a piece of unglazed porcelain.. Streak can be used only for minerals with a Mohs hardness of 7 or less, as minerals with a hardness greater than 7 will themselves scratch the streak plate. LUSTRE Lustre refers to the way in which the surface of a mineral reflects light, and is controlled by the kinds of atoms present and their bonding. It is described by the following terms: Adamantine – diamond-like lustre; such minerals are usually transparent and have a high refractive index; e.g. diamond, cerussite, cubic zirconia Dull or Earthy – no reflections; e.g. kaolinite
larger crystalline Quartz, and an outer layer of Chalcedony or banded Agate. PHYSICAL PROPERTIES OF QUARTZ CHEMICAL FORMULA SiO 2 COMPOSITION Silicon Dioxide COLOR Colorless, white, purple, pink, brown, and black. Also, gray, green orange, yellow, blue, and red. Sometimes multicolored or banded. STREAK White HARDNESS 7 CRYSTAL SYSTEM Hexagonal 3D CRYSTAL ATLAS CRYSTAL FORMS AND AGGREGATES Crystals, which are hexagonal in shape, vary in shape and size. Quartz crystals are unique and very identifiable with their pointed and often uneven terminations. Crystals can be in enormous prismatic and stubby crystals, or in pointed aggregates of such crystals. Crystals are usually striated horizontally, and are sometimes doubly terminated. Quartz crystal habits include drusy, grainy, bladed, as linings of geodes, as rounded waterworn pebbles, radiating, as pointy pyramids on a matrix, as dense agglomerations of small crystals, massive, globular, stalactitic, crusty, in nodules, and in amygdules. Crystals frequently twin; a famous twinning habit is the Japanese twin, where two crystals contact at a 90° angle. Quartz crystals may also contain a scepter growth, where the top of a crystal bulges out from the rest of the crystal, and may also from as phantom
growth, where one crystal forms over another, leaving a ghosted form inside. The crystal structure of Quartz is very complicated. As a result of a changeover from alpha to beta Quartz, crystals form as hexagonal prisms with modified crystal faces. TRANSPARENCY Transparent to opaque SPECIFIC GRAVITY
LUSTER
Vitreous. Transparent, colorless Quartz crystals from a few distinct localities may be adamantine. CLEAVAGE Indiscernible. Seldom exhibits parting. FRACTURE Conchoidal TENACITY Brittle OTHER ID MARKS 1) Some specimens fluoresce, especially white and green.
- Triboluminescent.
- Piezoelectric. COMPLEX TESTS Dissolves in hydrofluoric acid IN GROUP Silicates; Tectosilicates; Silica Group STRIKING FEATURES Hardness, crystal forms, striations on crystal faces, and frequent appearance of conchoidal fractures on crystal faces. ENVIRONMENT Quartz occurs in almost every single mineral environment. ROCK TYPE Igneous, Sedimentary, Metamorphic POPULARITY (1-4) 1 PREVALENCE (1-3) 1 DEMAND (1-3) 1 VARIETIES FOR AMETHYST, CITRINE, AND CHALCEDONY ARE LISTED SEPARATELY: AMETHYST – purple variety of Quartz. AVENTURINE – opaque form of compact Quartz or Chalcedony containing small
Herkimer Diamond crystals are usually doubly terminated and short. MILKY QUARTZ – white, translucent to opaque variety of Quartz.
MORION –
opaque form of black quartz. A type of Smoky Quartz. PHANT O M QUARTZ
quartz containing internal phantom growths, or ghostlike layers within a crystal.
PRASE –
light to emerald green, transparent to translucent Quartz, with coloring caused from inclusions of green minerals, such as Actinolite, Hedenbergite, Chlorite, or Malachite. PRASEME
- light green, translucent form of Quartz with Hedenbergite inclusions found on Serifos Island, Greece.
PRASIOLITE
- describes a light green quartz artificially colored by heat treatment of certain types of Amethyst. May also be called Green Amethyst by some jewelers.
RAINBOW QUARTZ – quartz synthetically colored with an iridescent layer formed from gold or other metals. Also see Aqua Aura.
ROC
K CRYSTAL
colorless, transparent variety of quartz in large crystal form. ROSE QUARTZ – pink variety of Quartz.
RUTILATED
QUARTZ –
quartz with golden yellow, needle-like Rutile inclusions. SCEPTER QUARTZ – quartz crystal with scepter like protusion on the end of the crystal that is wider than the rest of the crystal.
SMOKY
QUARTZ – brown to black, “smoky” variety of Quartz. STAR QUARTZ – polished quartz displaying asterism in the form of a six- rayed star.
TOURMALIN
A TED QUARTZ –
quartz with splintery tourmaline inclusions. FELDSPAR Feldspar is the name of a large organization of rockforming silicate minerals that make up over 50% of Earth’s crust. They are discovered in igneous, metamorphic, and sedimentary rocks in all components of the sector. Feldspar minerals have very comparable structures, chemical compositions, and bodily properties. Common feldspars consist orthoclase (KAISi3O8), albite (NaAISi3O8), and anorthite (CaAI2Si2O8).
The plagioclase feldspars are triclinic. The plagioclase series follows (with percent anorthite in parentheses): Albite (0 to 10) NaAISI3O8, Oligoclase (10 to 30) (Na, Ca) (AI, Si) AISi2O8, Andesine (30 to 50) NaAlSi3O8—CaAl2Si2O8, Labradorite (50 to 70) (Ca,Na)Al(Al,Si)Si2O8, Bytownite (70 to 90) (NaSi,CaAl)AlSi2O8, Anorthite (90 to 100) CaAl2Si2O8. AUGITE Augite is isomorphous with the minerals Diopside and Hedenbergite. It is an intermediary member between these minerals, forming a series, but contains additional sodium and aluminum within its chemical structure. Strictly speaking, because of the variables in its chemical structure, Augite is really more of a group then a single mineral, but still classified a single mineral species by the IMA. PHYSICAL PROPERTIES OF AUGITE CHEMICAL FORMULA (Ca,Na)(Mg,Fe,Al)(Al,Si)2O COMPOSITION Silicate of calcium, sodium, magnesium, iron, and aluminum. Occasssionally with zinc, manganese, and titanium impurities. VARIABLE FORMULA (Ca,Na)(Mg,Fe,Al,Zn,Mn,Ti)(Al,Si)2O COLOR Green, grayish-green, greenish brown, dark brown, black STREAK Light green to colorless HARDNESS 5 – 6 CRYSTAL SYSTEM Monoclinic 3D CRYSTAL ATLAS CRYSTAL FORMS AND AGGREGATES Often as prismatic crystals with a rectangular or octagonal cross section. Also in short, stubby crystals with a flattened slightly pyramidal termination. Other forms are columnar, grainy, massive, fibrous, and in disordered aggregates of rectangular crystals. May also be in penetration twins with v-shaped saddles. Crystals from certain localities have
partially hollow etchings. TRANSPARENC Y Opaque. Translucent in thin sections. SPECIFIC GRAVITY
LUSTER Vitreous, dull CLEAVAGE 1,2 – prismatic at cleavage angles of 87° and 93° (Characteristics of minerals in the pyroxene group). May also exhibit parting in one direction. FRACTURE Uneven to splintery TENACITY Brittle IN GROUP Silicates; Inosilicates; Pyroxene Group STRIKING FEATURES Color, crystal habits, cleavage, and environment ENVIRONMENT An important constituent of many igneous rocks, including basalt, diabase, and gabbro. Also, in carbonatite and nepheline syenite pegmatites, and in metamorphic Serpentine deposits. ROCK TYPE Igneous, Metamorphic POPULARITY (1-4)
PREVALENCE
DEMAND (1-3) 2
VARIETIES FASSAITE – variety of augite originally described from the Val D’ Fassa region in Italy which has a low iron content. This is usually responsible for this variety having a lighter green color and increased translucency then other most Augite. JEFFERSONITE – varieties of Augite rich in manganese and zinc, found in the Franklin District, Sussex Co., New Jersey and surrounding areas in the Franklin marble. Its chemical formula is Ca(Mn,Zn,Fe)Si2O6. URALITE – Pseudomorph of Actinolite after any mineral of the pyroxene group, especially Augite. HORNBLENDE
CRYSTAL SYSTEM Very little industrial use BIOTITE Biotite is a very common form of mica. It is named in honor Jean Baptiste Biot (1774 - 1862), a French physicist, mathematician, and astronomer who researched the mica minerals for their optical properties. Because of Biotite's abundance, its presence is usually lacking in collections except for it being an accessory mineral to other minerals. Biotite can come in enormous crystal sheets that can weigh several hundred pounds. Thin sheets can be peeled off as layers, and the thinner a layer is peeled the greater its transparency becomes. In 1998, the IMA removed the status of Biotite as an individual mineral species, and instead declared it as a group name for the following individual members: Phlogopite, Annite, Siderophyllite, and Eastonite. However, mineral collectors still refer to Biotite by its traditional name and rarely make a distinction among its members except for Phlogopite. Biotite is very hard to clean because if washed it will absorb water internally and start to break apart. The best way to wash Biotite and other Micas is with a dry electric toothbrush. PHYSICAL PROPERTIES OF BIOTITE CHEMICA L FORMULA The classic formula for Biotite is: K(Mg,Fe2+3) (Al,Fe3+)Si3O10(OH,F) The group formula including all member minerals: K(Mg,Fe2+)3(Al,Fe3+)(Al,Si)3O10 Individual members are: Phlogopite: KMg3AlSi3O10)(F,OH)2 Siderophyllite: KFe2+2Al(AlSi2O10)(OH)2 Eastonite: KMg2Al(AlSi2O10) (OH)2 Annite: KFe2+3AlSi3O10(OH)2 Fluorannite: KFe2+3AlSi3O10)F Tetraferriannite: K(Fe2+3Mg)(Fe3+,Al)Si3O10)(OH) COMPOSI TION Basic fluoro potassium, magnesium, iron aluminum silicate COLOR Black, dark brown, dark green, reddish black. Individual group member minerals such as Phlogopite and Eastonite
can be in lighter colors. STREAK White HARDNES S
CRYSTAL
SYSTEM
Monoclinic 3D CRYSTAL ATLAS CRYSTAL FORMS AND AGGREGATES Crystals are in thick flakes, micaceous masses and groupings, and in tabular, foliated, flaky, and scalyforms. Crystals may also be elongated with one dimension flat, or stubby triangular or hexagonally shaped crystals. Also forms in prismatic barrel- shaped or tapered pyramid- shaped crystals composed of dense parallel plates, and as rounded nodules of dense crystals. TRANSPARENC Y Translucent to opaque. Thin flakes will always be translucent if held up to the light. SPECIFIC GRAVITY
LUSTER Pearly CLEAVAGE 1, 1 FRACTURE Uneven TENACITY Sectile, elastic OTHER ID MARKS Tendency for small pieces or flakes or peel off. IN GROUP Silicates; Phyllosilicates; Mica Group STRIKING FEATURES Flaky habit, crystals, sectility, and mode of occurence ENVIRONMENT Biotite is a common rock-forming mineral, and is especially noted in metamorphic rocks such as schist and gneiss. It is also found in igneous rock such as
