Diamond （鑽石）
Formation of Diamonds 鑽石的形成
- Can be found from Lithosphere to Lower Mantle (岩石圈至下地幔)
- With High PT conditions, crystallization occur
- Lithospheric diamond (岩石圈鑽石)
- type 1a: colorless/ with yellowish impurities
- occur at 150-200km beneath the Earth’s surface
- Super deep diamonds (超深層鑽石)
- type 2: colorless/ with pink, red, brown
- within mantle rise up through Kimberlite Magma （金伯利岩), with diamonds inside as transporting agent
- occur at two levels (upper mantle to transition zone 250-400km and lower mantle 600-800km)
Ruby (紅寶石）
About Ruby
- Red variety of Corundum (Al₂O₃, 剛玉), with Chromium (Cr, 鉻) giving the color red
- Substitute Aluminum (Al, 鋁) and integrated to crystal lattice
- Have a strong red fluorescence (螢光) when exposed to Ultraviolet light (UV, 紫外線)
- The presence of Iron can diminish the fluorescence
Formation of Ruby 紅寶石的形成
- Needed condition :
- Corundum with traces of Chromium= Ruby
- HIGH PT condition (Metamorphic Rocks 變質岩)
- Al₂O₃ + Cr –> Ruby
- Aluminium rich rock interact with Chromium rich rock
- Formed in Mica Schists (雲母片岩) + Ultramafic Greenstones (超鎂鐵質綠岩)
Sapphire (藍寶石）
About Sapphire
- Blue variety of Corundum (Al₂O₃), with Iron (Fe²⁺) and Titanium (Ti⁴⁺,鈦) giving the color blue
- Substitute Aluminum (Al) and integrated to crystal lattice
- Pure corundum is colorless (無色)
- Interacted through inter valence charge transfer (IVCT, 間隔電荷轉移), iron can exist as Fe²⁺ or Fe³⁺ valency state
Formation of Sapphire 藍寶石的形成
- Formed by Metamorphism (變質作用, High pressure and temperature)
- Rich in Al + Fe and Ti
- Primary deposit (原生沉積) : from magmatic and metamorphic rocks
- Secondary Deposit (二次沉積) : By erosion and weathering (侵蝕和風化), river beds
Emerald (祖母綠)
About Emerald
- The green variety of Beryl (Be3Al2Si6O18, 綠柱石)
- Beryl is colorless
- coloured by traces of Chromium (Cr,鉻) and Vanadium(V, 釩)
- Cyclosilicate mineral (環狀矽酸鹽礦物)
Formation of Emerald 祖母綠的形成
- Emerald form at the rim of magma chamber (岩漿房邊緣) inside magmatic rocks (岩漿岩).
- Pegmatitic pod (偉晶岩莢)= Large mineral cluster (簇), Pegmatites form from waters that separate from a magma in the late stages of crystallization(like Quartz Vein (石英脈) which allow hydrothermal fluid (熱液) to pass through)
- Beryllium (鈹) in magmatic Granite as fluid fill in the pematitic pods
- Chromium from hydrothermal fluid percolate from mafic schist (從鎂鐵質片岩中滲出)
- Combination of metamorphism/ metasomatism (reaction with fluid, 交代作用) and Crystallisation of Magma
Opal (蛋白石）
About Opal
- Forms over long periods through silica derived from sedimentary rocks （沉積岩的二氧化矽）
- silica dissolves and is transported as a gel by water
- Opal develops when the silica gel seeps into cracks or voids in rocks
- Represented by the formula SiO₂ 。n(H₂O)
