WEEK 2 - Minerals & Gems Flashcards
What is a Mineral?
Defining Features of a Mineral:
- Naturally occurring (not man-made).
- Solid (not liquid or gas).
- Inorganic (not from living things).
- Has a definite chemical composition (specific elements in a fixed ratio).
- Crystalline structure (atoms arranged in an orderly pattern).
- Ice is considered a mineral
- Most rocks are made of aggregated mineral crystals or particles
What are Minerals Made Of?
Minerals = Elements – They are composed of chemical elements.
Elements Defined – Cannot be broken down into simpler substances.
Common Elements in Minerals – Hydrogen, helium, oxygen, carbon, calcium.
Not Minerals! – Manganese, selenium, chromium are elements, not minerals.
How Many Elements Exist? – Over 100 elements, with 92 naturally found on Earth.
Atomic Structure
Atom - The smallest unit of matter that keeps an element’s properties
Nucleus - Center of the atom, made of protons (+) and neutrons (0) (most of the atoms mass)
Electrons - Orbit around the nucleus in cloud-like shells, defining energy levels
Valence Electrons - Found in the outermost shell, important for bonding
Subatomic Particles
The smaller building blocks of an atom, the three main types are:
Proton – Charge: +1, Mass: 1
Neutron – Charge: 0, Mass: 1 (stabilize the nucleus)
Electron – Charge: -1, Mass: almost 0
Periodic Table of Elements
Elements are organized according to their weight and other characteristics
How Are Elements Shown in the Periodic Table?
Atomic Number = # of Protons – Every element has a set number of protons (Carbon = 6)
Element Symbol – Abbreviation of the element’s name (C = Carbon)
Atomic Weight – Total mass of protons, neutrons, and electrons (Carbon ≈ 12.011)
Element Name – Full name of the element (e.g., Carbon)
Why Do Atoms Bond?
Electron Shells Need to Be Full – Atoms want full outer shells for stability
Shell Capacity – Inner shell = 2 electrons, Outer shells = 8 electrons
Unfilled Shells = Bonding – Atoms share, gain, or lose electrons to become stable
Ionic Bonding: The Electron Exchange
How It Works – One atom gives away electrons, another takes them
Positive Ion (Cation) – Loses electrons (e.g., Sodium Na⁺)
Negative Ion (Anion) – Gains electrons (e.g., Chlorine Cl⁻)
Why? – This creates a strong attraction between oppositely charged ions
Example:
Sodium (Na) + Chlorine (Cl) = Table Salt (NaCl)
Sodium Gives an Electron – Becomes Na⁺ (positive ion)
Chlorine Accepts It – Becomes Cl⁻ (negative ion)
Result = Ionic Bond – Opposites attract, forming NaCl (salt)!
How Does Salt (Halite) Form?
Opposites Attract – Positive sodium ions (Na⁺) bond with negative chloride ions (Cl⁻)
Forms Sodium Chloride (NaCl) – A mineral called Halite
Halite = Table Salt – The same salt we eat!
How Do Atoms Share Electrons? (Covalent Bonding)
When Two Atoms Want More Electrons – Instead of giving them away, they share!
Example: Two Chlorine Atoms (Cl₂) – Each has 7 outer electrons and needs 1 more
Solution: They Share One Electron Each – This forms a covalent bond, creating a chlorine molecule (Cl₂)
How Does Salt (Halite) Get Its Shape?
Ionic Bonding Creates a Cube Structure – Sodium and chloride ions arrange in a repeating pattern
This Regular Pattern = Crystal Shape – This is why salt forms cubic crystals
Covalent Bonding in Minerals
Some Minerals Are Also Covalently Bonded – Example: Diamonds 💎
Diamond = Pure Carbon (C) – Each carbon atom shares electrons with 4 others, creating an extremely strong covalent structure
What If Two Atoms Want Electrons?
Example: Two Chlorine Atoms
Each chlorine has 7 electrons in its outer shell
They need 1 more to reach 8
Solution: They SHARE electrons → This forms a Covalent Bond!
Intermolecular Bonding (Weak Attractions)
What is Intermolecular Bonding? – Weak forces between molecules (not inside them)
Example: Water Molecules 💧 – The slightly positive hydrogen in one water molecule attracts the slightly negative oxygen in another, forming weak “van der Waals” forces
These Bonds Are Easy to Break – This is why water flows easily and evaporates with heat
Mineral Properties (What Determines Them?)
Chemical composition & crystal structure define appearance & behavior
Lab tests can identify minerals, but they are expensive & time-consuming
Some minerals are valued for their beauty & usefulness (e.g., gems 💎)
Quartz: A Covalent Mineral
Quartz = Silica (Silicon + Oxygen)
Each Silicon (Si) atom bonds with 4 Oxygen (O) atoms
Oxygen atoms share electrons with Silicon, forming a strong covalent network
This structure gives Quartz its hardness and crystal shape
Intermolecular Bonding in Minerals
Graphite (in Pencils ✏️) - Carbon atoms have strong covalent bonds, but weak forces hold the layers together
- These weak bonds make graphite layers rub off easily on paper
Mica Minerals (Flaky Appearance) - Mica has strong covalent bonds within layers, but weak forces between layers, making it peel in thin sheets
Metallic Bonding (How Metals Stay Strong & Conduct Electricity ⚡)
What is Metallic Bonding? – Metal atoms “float” in a sea of free electrons, allowing easy movement
Why Are Metals So Conductive? – Free-moving electrons carry electricity (like in copper wires 🧵🔌)
Metals Are Malleable – Because the atoms can slide past each other, metals can be shaped easily (like gold and silver jewelry 💍)
Why Do Mineral’s Have Specific Shapes?
Atoms arrange in patterns that form distinct crystal shapes
The way atoms pack together determines a mineral’s external geometry
Examples of Crystal Forms/Shapes
Halite (NaCl - Table Salt) 🧂 → Cubic shape
Quartz (SiO₂) ⬡ → Hexagonal prisms
Diamond (C) 💎 → Octahedra (sometimes cubes)
Minerals aren’t just random chunks—their atomic structure gives them unique geometric shapes! 🔷
Cleavage
How minerals break apart
What is Cleavage?
Minerals break along weak atomic bonds, forming smooth surfaces
This breakage follows specific planes in the crystal structure
Example: Mica Minerals ✂️
- One-directional cleavage due to weak bonds between atom layers
- This gives mica its sheet-like structure (used in glitter ✨)
Multiple Cleavage Directions
Some minerals have more than one cleavage direction:
- Fluorite 🟣 → 4 cleavage directions (octahedral)
H- alite (NaCl) 🧂 → 3 cleavage directions at 90° (cubic)
- Calcite ⚪ → 3 cleavage directions NOT at 90° (rhombohedral)
Cleavage Planes vs. Crystal Faces
Key Differences:
Crystal Faces = external shape of a mineral.
Cleavage Planes = internal breakage pattern along weak atomic bonds
Crystals keep their shape, but cleavage happens predictably along weak planes
💡 Example: Quartz (left) has a distinct crystal shape, but doesn’t cleave easily like calcite (right)
Fracture
How minerals break without cleavage
What is Fracture?
Some minerals don’t break along cleavage planes because their atomic bonds are evenly strong in all directions
Instead, they fracture in irregular patterns
Two Types of Fracture
- Conchoidal Fracture:
Scoop-shaped, curved surfaces (like a seashell 🐚)
- Example: Quartz breaks this way - Uneven Fracture:
Rough, irregular breakage in minerals with some cleavage but no distinct weak planes
- Example: Orthoclase feldspar
Difference Between Cleavage & Fracture
Cleavage → Flat, shiny surfaces (predictable breakage)
Fracture → Dull, rough, or curved surfaces (random breakage)
Hardness
Measures how resistant a mineral is so scratching
Harder minerals scratch softer ones, but softer ones can’t scratch harder ones
Depends on bond strength within the crystal
Mohs Scale of Hardness
💎 10 – Diamond (hardest)
🪨 7 – Quartz (common hard mineral)
🔪 5.5 – Glass & pocketknife
🪙 3 – Calcite (penny hardness)
☁️ 1 – Talc (softest)
- NOT A LINEAR SYSTEM
Determining Hardness in Minerals
✔ Test minerals by scratching them against materials of known hardness
✔ If a mineral scratches fluorite (4) but not calcite (3), it has a hardness between 3-4
✔ Use fingernail (2.5), penny (3), or glass (5.5) to test unknown minerals
Specific Gravity in Minerals
A measure of how heavy a mineral is compared to an equal volume of water
Formula: Weight of mineral / Weight of equal volume of water
Example: If a mineral weighs 3 times as much as an equal volume of water, its specific gravity is 3
Mineral Weight within Specific Gravity
Some minerals feel heavier than others due to their specific gravity
Helps in identifying similar-looking minerals with different densities
Example:
- Barite (BaSO4): Specific gravity of 4.50 (feels heavy)
- Quartz: Specific gravity of 2.65 (feels light)
Diaphaneity in Minerals
The ability to transmit light:
- Transparent: Light passes through without distortion (like clear glass).
Example: Quartz
- Translucent: Light passes through but scatters (like frosted glass or milk).
Example: Quartz (milky appearance)
- Opaque: Light does not pass through at all (like metal).
Example: Meyerhofferite
Lustre in Minerals
Lustre is the way light reflects off the surface of a mineral
Two Main Types of Lustre
- Metallic: Minerals that look like metal, often shiny and reflective
- Non-Metallic: Minerals that do not have a metallic appearance; they can be glassy, dull, or pearly
Examples of The Types of Lustre
- Metallic:
Gold – Bright, reflective, and shiny.
Pyrite – Resembles metal, often called “Fool’s Gold.” - Non-Metallic:
Fluorite – Glassy and transparent.
Calcite – Can be transparent or pearly.
Tourmaline – Can be dark and dull or shiny with a non-metallic sheen.
Colour in Minerals
Colour is caused by the chemical composition of a mineral
Some minerals have a distinct colour (e.g., Azurite is deep blue, Pyrite is brassy yellow)
However, colour can be misleading due to impurities (e.g., pure Quartz is clear, but impurities can turn it purple like Amethyst or yellow like Citrine)
Causes of Colour
Colour changes in minerals are due to the behavior of charged ions
Example: Amethyst gets its purple colour from ferric iron (Fe³⁺) impurities and radiation knocking out an electron
Absorbed light determines the visible colour (e.g., yellow light absorbed → purple appears)
Streak Test - Colour
Streak is the colour of the powdered form of a mineral
Hematite always produces a reddish-brown streak, even if the mineral itself looks metallic or dull
The streak test helps differentiate minerals with similar appearances
Magnetism in Minerals
Some minerals, like Magnetite, are naturally magnetic
Lodestone is a special variety of magnetite that strongly attracts iron objects
Ancient compasses used lodestone for navigation
Mineral Reaction with Acid
Some minerals effervesce (fizz) when exposed to acid
Calcite is the only mineral that strongly reacts with acid
This property is useful for identifying carbonate minerals
Optical Properties of Minerals
Some minerals, like Calcite, exhibit birefringence (double refraction), splitting light into two
Other properties like taste (Halite = salty), smell (Sphalerite = rotten eggs when heated), and texture (Talc = slippery) can help in mineral identification
Use of Physical Properties in Identification
Minerals can often be identified based on a combination of properties
A single property, like colour, is not always reliable
Example:
- Biotite and Amphibole are both dark, but their cleavage and hardness help distinguish them.
Gemology
The study of gem’s
Most closely aligned with mineralogy, drawing on chemistry, physics and geology
Physics and Chemistry of Minerals
Minerals have physical, chemical, and optical properties that help identify and classify them
These properties determine how minerals interact with light, heat, and other elements
Geology and Gemstones
Geology helps determine how gemstones form and where they can be found
It includes gem testing, cutting, polishing, and synthetic gem production
Also involves grading, marketing, and selling of precious metals and gemstones
What is a Gemstone vs a Gem?
GEMSTONE: Any ornamental stone used for personal adornment (jewelry, accessories)
GEM: A gemstone that has been cut and polished to enhance its beauty (includes pearls)
Two Types of Gemstones
- Precious Gemstones: High beauty, durability, stability, large size, and rarity
- Semiprecious Gemstones: Have only one or two of the above qualities
How Many Minerals Qualify as Gemstones?
Out of 4,000+ minerals, about 70 are gemstones
15-20 gemstones are commonly encountered by consumers
Most Valued Gems in the Marketplace
Diamonds, rubies, sapphires, emeralds, and some varieties of opal
Large, high-quality semiprecious gems can also be sold at high prices
Tourmaline Gem
Tourmaline is a semiprecious (valuable but not as rare or precious) gemstone
Large, colorful crystals of tourmaline can be very valuable
What Determines a Gemstone’s Value?
The value of both precious and semiprecious gemstones is based on:
- Beauty
- Durability
- Stability
Beauty in Gemstones
Beauty is subjective and varies from person to person
The beauty of a gem is based on colour, lustre, transparency, or unique optical properties
Example:
- Ammolite (a newly recognized gemstone) is valued for its beautiful colours
How is the Beauty of a Gemstone Measured?
50-60% of a gem’s value comes from its colour
20-30% is based on clarity (how free it is from imperfections)
10-20% is based on its cut (how well it is shaped and polished)
Exception: Diamonds value clarity and cut more than colour
What is Durability in Gemstones?
Durability refers to a gemstone’s ability to resist damage
It depends on hardness and tenacity (how tough it is against scratches and breakage)
The Four “C’s: Gemstone Value
The “Four Cs” (Carat, Colour, Clarity, Cut) determine the value of clear gemstones
What is Hardness in Gemstones?
Hardness is a gemstone’s resistance to scratching
Example:
- Ammolite is beautiful but has low hardness (3.5-4 on Mohs scale)
- Diamond is the hardest mineral (cannot be scratched by any other material).
What is Tenacity in Gemstones?
Measures how resistant a gemstone is to breaking or bending
Even if a gemstone is hard, it may still be brittle and break easily
Example:
- Nephrite Jade is not very hard but is very tough and resists breaking.
Hardness vs Tenacity in Gemstones
Hardness does NOT mean strength—a gemstone can be extremely hard but still break easily
Tenacity is about durability—a gemstone with high tenacity resists breaking even if it is soft
Example:
- Diamond is hard but brittle, while Nephrite Jade is softer but very tough.
What is Stability in Gemstones?
Stability refers to a gemstone’s resistance to chemical destruction
Example:
- Calcite dissolves in acid, making it unsuitable as a gemstone
Stability can also refer to how well a gemstone retains its colour
Three Factors That Influence Gem Value
- Weight – Heavier gems are generally more valuable
- Rarity – Rare gems command higher prices
- Demand – High demand increases a gem’s value
Weight and Carat (ct)
A gem’s value depends on its weight
Carat (ct) is the standard unit of weight for gemstones
1 carat = 0.2 grams
Example:
- A 100-carat diamond sold for $8 million in 2003
Carat Weight vs. Size
Different gemstones have different densities, so the same carat weight can appear in different sizes
Example:
- A 1 ct diamond is smaller than a 1 ct sapphire
- A 1 ct sapphire is smaller than a 1 ct opal
Lesson: Carat weight alone doesn’t determine size—dimensions matter when setting gemstones
Cullinan Diamond (Largest Uncut Gem-Grade Diamond)
Weight: 3,106 carats (621 grams)
Discovered: 1902, Premier Mine (now Cullinan Diamond Mine), South Africa
Notable Feature: Had a structural flaw in the center
Processing: Cut into 3 pieces, then 9 major stones plus smaller fragments
Cullinan 1 (The Great Star of Africa)
Weight: 530 carats
Size: 5.5 x 4.5 x 2.5 cm
Value: Estimated at $400 million
Current Location: Tower of London, U.K., set in the Sceptre with the Cross of King Edward VII (part of the British Crown Jewels)
Cullinan II: A 317.4-carat stone set into the Imperial State Crown (British Crown Jewels)
Lesedi La Rona (2nd Largest Uncut Diamond)
Weight: 1,109 carats (221 grams)
Discovered: 2015, Karowe Mine, Botswana, by Lucara Diamond Corp
Sold: $53 million to Graff Jewellers in 2017
Cutting:
- Divided into Graff Lesedi La Rona (302.37 carats) and 66 smaller stones
- Largest emerald-cut diamond in the world
Rarity of Gemstones
Rarer gems = Higher price
Formed under unique geological conditions
More supply = Lower price
Bigger gems (higher carat weight) are rarer
Most expensive gems:
- Blue Diamond, Jadeite, Pink Diamond, Ruby, Emerald
Demand for Gemstones
Trends affect gemstone value
Victorian Era:
- Pyrope Garnet was popular, then lost value (red gemstone)
Turquoise Jewelry:
- Trend faded, then came back in the 1980s-90s
Buyers pay more when gems are “in fashion”
Turquoise
Found in natural form & jewelry
Southwestern U.S
Common in jewelry & fabric designs, showing its cultural importance
Turquoise = Hydrous phosphate of copper & aluminum
Misconceptions on Naming & Color Deception
Naming Issue: Gems historically grouped by color, not composition
Example 1: Ruby (Hardness 9) ≠ Spinel (Hardness 8) (mistaken as same) –> RED
Example 2: Citrine (Quartz) vs. Imperial Topaz (citrine sold as pricier topaz) –> YELLOW
Corundum
Hard mineral (Mohs 9), often dull; exceptional clarity/color used as gems
Asterism
Star-like light effect in some rubies & sapphires (star sapphire and star ruby) due to rutile (TiO₂) inclusions
What Makes Ruby?
Corundum with chromium → deep red color
What Makes Sapphire?
Any corundum color except red
Beryl Mineral
Beryl: Mineral with different colors
Emerald → Green variety of beryl
Aquamarine → Light blue variety of beryl
Gem Cutting & Polishing
Enhances beauty & value of gemstones
Three Basic Cuts of Gem Cutting and Polishing
- Cabochon → Smooth, rounded
- Brilliant Cut → Maximizes sparkle
- Step (Trap) Cut → Rectangular, layered look
Cabochon Cut - Gem
Smooth, rounded dome
Used for opaque/translucent gems (e.g., turquoise, opal)
Brilliant Cut - Gem
Maximizes sparkle by reflecting & dispersing light
Common in diamonds (up to 59 facets) but also used for tourmaline & tanzanite
Step (Trap) Cut - Gem
Rectangular, layered facets that enhance color
Less light dispersion (“fire”)
Used for amethyst, spinel, aquamarine
Emerald Cut (Step Cut Variant)
Special step cut for emeralds & diamonds
Reduces edge damage in emeralds & brittle gems
Preferred for flat diamond specimens to maximize usable material
