Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Identification Of Gemstones
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Identification Of Gemstones
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Subject: Mining
Class: Senior Secondary 2
Term: 1st Term
Week: 7
Theme: Gemology And Lapidary
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
Mention the effective methods of gemstone identification. Identify common varieties of gemstones in hand specimen and in the laboratory.
Gemology And Lapidary objectives. Introduce the performance objectives for the lesson.
2. Explanation of Gemstone Identification Methods (30 minutes): Systematically explain each identification method, starting with visual inspection and moving to physical properties.
Use visual aids: charts (Mohs scale, luster types), diagrams (crystal habits), and clear photographs of inclusions.
Demonstration of Hardness Test: Using readily available materials: fingernail (2.5), copper coin (3.5), steel knife/nail (5.5-6), piece of glass (5.5), and a known quartz crystal (7) if available. Demonstrate how to safely test an unknown sample against these known standards, emphasizing scratching an inconspicuous area. Practical
Example: Demonstrate scratching a piece of glass with a known quartz sample to show it leaves a mark. Then, try to scratch the quartz with the glass, showing it does not. Demonstration of Specific Gravity (if possible): If a sensitive balance is available, demonstrate the weighing in air and water method using a known sample (e.g., a common stone, a metal object). Explain the calculation step-by-step. If not, explain the concept and show the formula. Explain other properties (colour, luster, transparency, cleavage, fracture, streak) using examples and clear descriptions. Briefly explain the concepts of optical properties (RI, birefringence, dispersion, pleochroism, fluorescence) and inclusions, emphasizing their diagnostic value even if instruments are not available. Show pictures of what double refraction or typical inclusions look like under magnification.
3. Identification of Common Varieties (20 minutes): For 3-4 common gemstones (e.g., Quartz, Tourmaline, Garnet, Sapphire - especially those found in Nigeria), present a summary of their key identifying features based on the methods just taught. Use a table format to compare their properties (e.g., hardness, specific gravity, typical colour, crystal habit). Show actual samples or high-quality images of these gemstones (both rough and cut) and highlight their distinguishing characteristics.
4. Facilitate Group Activity (20 minutes): Divide students into small groups.
Provide each group with either: Actual specimens (if available): 2-3 unknown samples (e.g., clear glass, quartz, piece of common rock/mineral). OR detailed descriptive cards for 2-3 hypothetical "unknown" gemstones, listing their properties (e.g., "Sample A: green, vitreous luster, scratches glass but not quartz, SG 3.1, prismatic crystals"). Instruct groups to use the learned methods (visual inspection, hardness test – if samples are available, or analysis of descriptive properties) to attempt to identify their samples/descriptions.
5. Review and Consolidation (10 minutes): Address common misconceptions. Summarize the key identification methods. Reiterate the importance of combining multiple tests.
Student Activities:
1. Actively listen and take notes during the teacher's explanations.
2. Participate in brainstorming and Q&A sessions.
3. Observe demonstrations of hardness and specific gravity tests keenly.
4. In groups, examine provided samples (or descriptive cards) and discuss observable properties.
5. If samples are available, practice simple hardness tests on inconspicuous areas or designated "scratch plates" (e.g., glass, unglazed ceramic tile, known quartz pieces).
6. Collaboratively attempt to identify their assigned samples/descriptions using the taught methods.
7. Present their findings and reasoning to the class.
8. Ask clarifying questions during review.
4. Guided Practice (With Solutions)
Question 1: A student finds a transparent purple crystal in a mining area in Nasarawa State. It has a glassy luster and hexagonal prism shape. When tested, it easily scratches a piece of common window glass. a) What is the likely hardness range of this mineral based on the scratch test? b) Which common gemstone, often found in Nigeria, fits this description? c) What additional non-destructive test could provide further confirmation?
Solution 1: a)
Hardness Range: Common window glass has a Mohs hardness of approximately 5.
5. Since the gemstone easily scratches the glass, its hardness is greater than 5.
5. Given its natural occurrence and crystal form, it likely has a hardness around 7, as it's a common characteristic of minerals that scratch glass effectively. b)
Common Gemstone: The description (transparent purple, glassy luster, hexagonal prism, hardness > 5.5) strongly suggests Amethyst, which is a variety of Quartz. Quartz has a hardness of 7, a vitreous luster, often forms hexagonal prisms, and amethyst is famously purple. Nasarawa State is known for quartz deposits. hardness of approximately 5.
5. Since the gemstone easily scratches the glass, its hardness is greater than 5.
5. Given its natural occurrence and crystal form, it likely has a hardness around 7, as it's a common characteristic of minerals that scratch glass effectively. b)
Common Gemstone: The description (transparent purple, glassy luster, hexagonal prism, hardness > 5.5) strongly suggests Amethyst, which is a variety of Quartz. Quartz has a hardness of 7, a vitreous luster, often forms hexagonal prisms, and amethyst is famously purple. Nasarawa State is known for quartz deposits. c)
Additional Non-Destructive Test: Observing for conchoidal fracture if a small chip or broken piece is available. Another key property for confirmation would be to try to scratch a known quartz sample (hardness 7); if it does not scratch the quartz, then its hardness is indeed around 7, confirming quartz. Measuring Specific Gravity (SG) would also be highly diagnostic, as quartz has a consistent SG of 2.65. --- Question 2: An artisanal miner brings a small, intensely red stone to a buyer in Kaduna. The stone is quite heavy for its size and has a vitreous luster. When tested, it scratches quartz but is itself scratched by a sapphire. a) Estimate the Mohs hardness of this red stone. b) Based on its hardness, colour, and density (heavy for its size), suggest two possible natural gemstone candidates. c) How could one definitively distinguish between the two candidates if one is single refractive and the other is doubly refractive?
Solution 2: a)
Mohs Hardness: Quartz has a Mohs hardness of
7. Sapphire has a Mohs hardness of
9. Since the stone scratches quartz (meaning >7) but is scratched by sapphire (meaning <9), its Mohs hardness is between 7 and 9. b)
Possible Gemstone Candidates: Spinel: Hardness 8, often red (though various colours), vitreous luster, SG ~3.
6. Topaz: Hardness 8, can be red (imperial topaz), vitreous luster, SG ~3.
5. Garnet (e.g., Pyrope or Almandine): Hardness 6.5-7.5 (some may scratch quartz but might be on the lower end of the "scratched by sapphire" range), often red, vitreous, SG ~3.7-4.3 (fits "heavy for its size"). (Teacher's note: For SS2, focusing on Spinel and Topaz is more direct given the hardness bracket, but Garnet is a good alternative to consider, especially common red ones that are quite hard.) c) Distinguishing between Single and Doubly Refractive Gems: A polariscope is the ideal instrument to distinguish between single refractive (isotropic) and doubly refractive (anisotropic) gems. A single refractive gem will remain dark when rotated between crossed polarizers, while a doubly refractive gem will show flashes of light (extinction and illumination). Without a polariscope, one might look through a faceted stone at a printed line: a doubled image of the line indicates double refraction (e.g., Topaz), while a single image suggests single refraction (e.g., Spinel or Garnet). This visual test is less precise but observable. --- Question 3: A dealer tries to sell a transparent, faceted yellow stone as "Nigerian Citrine" to a customer. The customer notices it has distinct striations on its surface and feels unusually heavy. a) What property is suggested by the stone feeling "unusually heavy" for its size? b) How would the specific gravity of true Citrine compare to a heavier, yellow gemstone that might be mistaken for it? c) If the customer suspects it might be Zircon, what key optical property (apart from colour) might help distinguish it from Citrine (Quartz)?
Solution 3: a) Property suggested by "unusually heavy": This suggests a higher Specific Gravity (SG) or density compared to what one might expect for a typical yellow gemstone of that size. b)
Specific Gravity Comparison: True Citrine (a variety of Quartz) has an SG of 2.
6
5. A heavier yellow gemstone, such as Zircon (SG 4.6-4.7) or Yellow Sapphire (SG 4.0), would have a significantly higher specific gravity. Thus, the specific gravity of the unknown stone would be much higher than that of true citrine. c) Distinguishing from Citrine (Quartz) if suspected to be Zircon: * Dispersion ("Fire"): Zircon has very strong dispersion (fire), much higher or density compared to what one might expect for a typical yellow gemstone of that size. b)
Specific Gravity Comparison: True Citrine (a variety of Quartz) has an SG of 2.
6
5. A heavier yellow gemstone, such as Zircon (SG 4.6-4.7) or Yellow Sapphire (SG 4.0), would have a significantly higher specific gravity. Thus, the specific gravity of the unknown stone would be much higher than that of true citrine. c) Distinguishing from Citrine (Quartz) if suspected to be Zircon: Dispersion ("Fire"): Zircon has very strong dispersion (fire), much higher than Citrine. A faceted Zircon will show pronounced flashes of spectral colours.
Birefringence (Double Refraction): Zircon is famously known for its high birefringence, which can often be observed as a distinct doubling of facet edges when looking through the stone with a loupe, especially for highly birefringent zircons. Citrine (Quartz) is also doubly refractive, but its birefringence is much lower, making the doubling effect less obvious or practically unobservable without instruments.
5. Independent Practice (Questions Only)
1. List three visual characteristics that can be observed without any specialized equipment and explain how each contributes to gemstone identification.
2. Explain the Mohs hardness scale. How can a miner use simple tools like a fingernail, a copper coin, and a steel knife to estimate the hardness of an unknown mineral in the field?
3. A gem trader in Kano is offered a batch of green stones. Some appear to be transparent, while others are opaque. Describe how the property of transparency helps in initial classification and what types of green gemstones might fall into each category.
4. A rough, black, elongated crystal found in Plateau State is noted to have a triangular cross-section. What common gemstone does this crystal habit suggest? What would be its approximate hardness?
5. You are given two clear, colourless faceted stones. Stone A feels light for its size, while Stone B feels noticeably heavy. Assuming both are natural gemstones, what property is likely different between them, and how would you quantify this difference without destroying the stones?
6. Why is colour alone often an insufficient property for definitive gemstone identification? Provide an example involving a common red gemstone.
7. Describe two different types of fractures that gemstones can exhibit, and name a gemstone or mineral commonly associated with each.
8. Distinguish between "cleavage" and "fracture" in gemstones, highlighting their significance in gem identification and durability.
9. What are inclusions? How can observing inclusions under magnification help in: a) Identifying a gemstone? b) Distinguishing between natural and synthetic gemstones?
1
0. A gemstone collector notices that a yellow gemstone appears much lighter yellow when viewed from one direction and almost brownish-yellow when viewed from another direction. What optical property is being observed, and what does it indicate about the gemstone?
6. Evaluation and Assessment Evaluation Guide: Recognize and identify common varieties of gemstones in hand specimen and under the microscope.
Formative Assessment:
1. Questioning: During explanations, ask direct questions (e.g., "What is the hardness of quartz?" "How would you describe the luster of glass?") to check immediate understanding.
2. Observation: Observe students during group activities, noting their ability to apply identification methods and collaborate effectively.
3. Quick Quiz (5 minutes): "Name three effective methods for gemstone identification." "If a stone scratches glass but not quartz, what is its approximate Mohs hardness?" "What is the term for a gemstone's ability to show different colours when viewed from different angles?"
4. Peer Assessment: Have groups assess each other's identification attempts during the group activity, providing constructive feedback.
Summative Assessment:
1. Practical Identification Test (Aligned with Evaluation Guide): Setup: Provide 3-5 labelled (e.g., "Sample X," "Sample Y") unknown specimens (or detailed descriptive cards if specimens are unavailable). Samples should include common varieties like quartz, glass, a harder stone like tourmaline or garnet, and possibly an opaque material like jasper.
Task: Students are to identify each sample using the learned identification methods (visual inspection, hardness test, specific gravity estimation, etc.) and state their reasoning. If actual specimens are used, provide scratch plates (glass, copper coin, steel nail, quartz). *Marking Scheme for Practical Test (per