Dɛn ne Olivine Crystal Nhyehyɛe?

Olivine ahwehwɛ nhyehyɛe no yɛ orthorhombic nhyehyɛe a silicon-oxygen tetrahedra (SiO4) a wɔatew wɔn ho no nam dade cations a ɛfa octahedral mmeae so na ɛka bom. Wobetumi ayɛ saa nhyehyɛe yi ho mfonini sɛ oxygen atɔm ahorow a ɛyɛ ahinanan a ɛbɛn-a ɛyɛ ma, a magnesium anaa dade ions ahyɛ octahedral voids no fã ma na tetrahedral voids no nkyem awotwe mu biako na silicon ahyɛ mu ma.

Olivine kuw no yɛ ahwehwɛ wɔ orthorhombic ahwehwɛ nhyehyɛe no mu wɔ ahunmu kuw Pbnm (a wɔsan frɛ no Pnma wɔ tebea foforo mu) ase. Saa mfitiase symmetry yi kyerɛkyerɛ sɛnea atɔm ahorow hyehyɛ wɔn ho wɔ ahwehwɛ lattice no mu na enya aboɔden abo no honam fam su so nkɛntɛnso tẽẽ.

Unit cell no kura formula units anan (Z=4) na ɛda axes abiɛsa a ɛnyɛ pɛ a ɛtwam wɔ anim tẽẽ adi. Wɔ forsterite (Mg2SiO4) fam no, lattice parameters a wɔtaa yɛ no bɛyɛ=4.75 Å, b=10.20 Å, ne c=5.98 Å. Wɔ fayalite (Fe2SiO4) mu no, saa nsusuwii ahorow yi trɛw kakra kɔ=4.82 Å, b=10.48 Å, ne c=6.09 Å esiane dade ionic radius kɛse nti sɛ wɔde toto magnesium ho a.

Pbnm ahunmu kuw din no da nhyehyɛe mu nsɛm a ɛho hia adi. Saa ahunmu kuw yi kura ahwehwɛ wimhyɛn ne inversion center, na ɛde symmetry anohyeto pɔtee bi ba atom gyinabea ahorow so. Oxygen gyinabea abiɛsa a ɛsono wɔ ahwehwɛ mu (O1, O2, O3) wɔ nhyehyɛe no mu, a O1 ne O2 da ahwehwɛ wimhyɛn so bere a O3 di gyinabea a ɛwɔ hɔ nyinaa a enni symmetry soronko.

Olivine nhyehyɛe no mfinimfini no, SiO40 tetrahedron a atew ne ho no da, baabi a silicon atɔm bi a ɛwɔ mfinimfini no bata oxygen atɔm anan a atwa ho ahyia ho wɔ covalent kwan so. Saa tetrahedra yi yɛ ahofadi koraa-wɔnkyɛ oxygen atom ne tetrahedra a ɛbemmɛn no, na wɔkyekyɛ olivine mu sɛ nesosilicate anaa orthosilicate. Si-O nkitahodi biara susuw bɛyɛ 1.63-1.66 Å na ɛda covalent su a emu yɛ den adi.

Tetrahedra no sesa wɔn kwankyerɛ, na ɛkyerɛ soro ne fam wɔ toatoa so a ɛne crystallographic c-axis no di nsɛ. Saa nhyehyɛe a ɛsesa yi ma akwan horow ba ɔdan no mu a dade cations betumi atra. Silicon ion no gye beae biako pɛ a ɛda nsow wɔ ahwehwɛ mu a ɛte ahwehwɛ wimhyɛn so, a ɛkyerɛ sɛ silicon atɔm a ɛwɔ nhyehyɛe no mu nyinaa nam symmetry dwumadi ahorow so wɔ abusuabɔ.

Dade cations (a mpɛn pii no Mg2+ anaa Fe2+) gye mmeae abien a ɛsono emu biara a ɛwɔ octahedral a wɔakyerɛw so sɛ M1 ne M2. M1 beae no te inversion center so na ɛyɛ octahedron a wɔakyinkyim kɛse a oxygen atɔm asia atwa ho ahyia. Dadeɛ-oxygen nkitahodi tenten wɔ M1 mu firi bɛyɛ 2.07-2.13 Å ma magnesium. M2 beae no da ahwehwɛ wimhyɛn so na ɛma octahedron kɛse a ɛyɛ daa a MO akwansin trɛw 2.04-2.21 Å.

Nsonsonoe a ɛda M1 ne M2 mmeae ntam no wɔ nkyerɛkyerɛmu titiriw wɔ sɛnea cations ahorow kyekyɛ wɔn ho wɔ nhyehyɛe no mu no ho. Wɔ magnesium-dade a ɛyɛ den ano aduru ntoatoaso no mu no, Mg2+ ne Fe2+ nkyerɛ beae a wɔpɛ pii-abien no nyinaa gye M1 ne M2 mmeae a enni paw a emu yɛ den. Nanso, wɔ olivines a ɛwɔ calcium-te sɛ monticellite (CaMgSiO4) mu no, Ca2+ ions akɛse no pɛ sɛ wɔhyɛn M2 mmeae a ɛtrɛw kɛse no mu bere a Mg2+ pɛ M1 gyinabea nketewa no.

olivine crystal structure

Ɔkwan foforo a wɔfa so kyerɛkyerɛ olivine nhyehyɛe mu si oxygen sublattice no so dua. Oxygen anions no yɛ bɛyɛ hexagonal close-packed (hcp) array a wɔaboaboa ano wɔ a-axis no so. Saa nhyehyɛe yi ma wonya scaffolding a silicon ne dade cations gyina so.

Wɔ saa hcp oxygen nhyehyɛe yi mu no, dade cations no hyɛ octahedral voids a ɛwɔ hɔ no fã ma, bere a silicon atom ahorow no gye tetrahedral voids no nkyem awotwe mu biako-awotwe. Saa beae a wɔpaw yi a wɔtra mu yi ma olivine stoichiometry a ɛyɛ M2SiO4 su no ba, baabi a M gyina hɔ ma divalent dade cations.

Oxygen atɔm biara kyekyere silicon biako ne dade atɔm abiɛsa, na ɛma ɛyɛ nhyehyɛe a ɛyɛ den a ɛwɔ afã abiɛsa-. Oxygen atɔm no nyɛ pɛ-oxygen gyinabea abiɛsa a ɛsono emu biara (O1, O2, O3) no wɔ nkitahodi tebea ne akwansin a ɛda atɔm a ɛbemmɛn no ntam a ɛsono kakra. Saa nsakraeɛ a ɛba oxygen mmeaeɛ yi boa ma nhyehyɛɛ no nyinaa yɛ den na ɛka nneɛma te sɛ ɔhyeɛ ntrɛmu ne nhyɛsoɔ.

Layers of edge-sharing octahedra trɛw kɔ pɛpɛɛpɛ ne (100) plane, cross-a SiO4 tetrahedra a atew ne ho no abɔ mu. Saa su a ɛwɔ ntoatoaso yi bɛyɛ nea ɛho hia titiriw wɔ nhyɛso a wɔde di dwuma ase, efisɛ ɛma wimhyɛn ahorow a ebetumi ahwe ase a ɛka olivine mfiridwuma ne asasewosow su ahorow a ɛwɔ Asase mantle mu no ba.

Olivine ahwehwɛ nhyehyɛe no ma ano aduru a ɛyɛ den a ɛkɔ so wɔ magnesium awiei-member forsterite (Mg2SiO4) ne dade awiei-member fayalite (Fe2SiO4) ntam. Saa afrafra a edi mũ yi wɔ hɔ efisɛ Mg2+ (ionic radius ~0.72 Å) ne Fe2+ (ionic radius ~0.77 Å) no yɛ soronko wɔ kɛseyɛ mu bɛyɛ 7% pɛ, na ɛma wotumi de wɔn ho si ananmu a wɔnyɛ hwee a wɔnkyinkyim ahwehwɛ nhyehyɛe no kɛse.

Wɔtaa da nneɛma a wɔahyehyɛ adi sɛ molar ɔha biara mu nkyem, te sɛ Fo₇₀ Fa3 (anaasɛ Fo₇ kɛkɛ), a ɛkyerɛ sɛ 70% forsterite ne 30% fayalite. Abɔdeɛ mu olivines a ɛfiri mafic abotan mu taa firi Fo5 kɔsi Fo20, berɛ a mantle olivines taa yɛ magnesian kɛseɛ, a nneɛma a wɔahyehyɛ no twa Fo10 kɔsi Fo22 ho hyia.

Ɛkame ayɛ sɛ lattice parameters no kɔ soro linearly bere a dade a ɛwɔ mu no. Bere a Fe2+ si Mg2+ ananmu no, unit cell no trɛw efisɛ dade kɛse a ɛsõ no pia atɔm ahorow no kɔ akyiri kakra. Saa abusuabɔ yi yɛ nea wotumi hyɛ ho nkɔm araa ma wobetumi de unit cell dimensions adi dwuma de ahu olivine a ɛwɔ mu no pɛpɛɛpɛ.

Sɛ Mg-Fe a wɔde si ananmu titiriw no da nkyɛn a, olivine nhyehyɛe betumi de cations afoforo kakraa bi aka ho. Calcium hyɛn nhyehyɛe no mu kakraa bi, na ɛpɛ M2 beae no. Manganese (wɔ tephroite mu no, Mn2SiO4) betumi asi magnesium anaa dade ananmu koraa. Nickel, chromium, ne ferric iron (Fe3+) mpo betumi asi mmeae a ɛwɔ octahedral no ananmu, ɛwom sɛ ɛyɛ kakraa bi de.

Olivine nhyehyɛe kɔ so yɛ nea ɛyɛ den wɔ nhyɛso ne ɔhyew tebea pɔtee bi mu nkutoo. Bere a emu dɔ kɔ soro wɔ Asase mu no, olivine nhyehyɛe no bɛyɛ nea ahoɔden nyɛ papa na ɛdan polymorphs a ɛyɛ den a ɛwɔ ahwehwɛ nhyehyɛe ahorow.

Wɔ bɛyɛ 410 km bun mu (a ɛne nhyɛsoɔ bɛyɛ 14 GPa hyia) no, olivine kɔ exothermic phase nsakraeɛ mu kɔ wadsleyite mu. Saa nsakrae yi fa nhyehyɛe foforo a ɛho hia ho wɔ baabi a oxygen sublattice no dan fi hexagonal close-packing kɔ nhyehyɛe a ɛyɛ cubic kɛse so. Wadsleyite kura orthorhombic symmetry nanso ɛfa spinel-te sɛ nhyehyɛe a wɔasesa a silicon atom binom wɔ octahedral nkitahodi mu.

Wɔ Asase mantle no mu tɔnn, a emu dɔ bɛyɛ kilomita 520 (18-20 GPa) no, wadsleyite dan ringwoodite, a ɛfa cubic spinel nhyehyɛe. Wɔ ringwoodite mu no, silicon nyinaa gye mmeae a ɛwɔ afã awotwe sen sɛ ɛbɛtra mmeae a ɛwɔ ahinanan. Saa nsakrae ahorow yi ma density kɔ soro mpofirim a asasewosow ho animdefo hu sɛ ɛyɛ nea ɛnkɔ so wɔ asasewosow asorɔkye ahoɔhare mu.

Nhyɛso a nsakrae ahorow yi ba no gyina ɔhyew ne nneɛma a ɛwom so. Olivine a dade-dɔɔso wom no dannan wɔ nhyɛso a ɛba fam mu sen ahorow a magnesium-dɔɔso wom no. Wɔ 800℃, forsterite kronkron dan wadsleyite wɔ 11.8 GPa, bere a wadsleyite-kɔ-ringwoodite nsakrae no ba wɔ soro 14 GPa. Dade awiei-member fayalite no huruw wadsleyite nhyehyɛe no koraa na ɛdannan tẽẽ kɔ ahrensite (dade-bearing ringwoodite analog) wɔ nhyɛso a ɛba fam mu.

olivine crystal structure

Olivine nhyehyeɛ no yɛ n’ade anisotropically wɔ nhyɛsoɔ a wɔde di dwuma-crystallographic akwankyerɛ ahodoɔ compress wɔ rate ahodoɔ mu. M2 octahedron no mia ntɛmntɛm sen M1 octahedron no wɔ nneɛma a wɔahyehyɛ nyinaa mu fi forsterite so kosi fayalite so. Saa nsonsonoeɛ nhyɛsoɔ yi ba ɛfiri sɛ M2 beaeɛ no wɔ mfitiaseɛ volume kɛseɛ ne nsakraeɛ kɛseɛ wɔ ne bonding nhyehyeɛ mu.

Single-crystal X-ray diffraction nhwehwɛmu a ɛkɔ 8 GPa da no adi sɛ M2-O nkitahodi tenten yɛ tiaa ntɛmntɛm sen M1-O nkitahodi wɔ nhyɛso ase. M1 octahedron no bɛyɛ nea wontumi nhyɛ no kɛse bere a dade a ɛwɔ mu no kɔ soro no, na ɛno ma ɛyɛ abirabɔ sɛ ɛma bulk modulus (nhyɛso a ɛko tia nyinaa) kɔ soro kakra fi forsterite so kɔ fayalite-a nea efi mu ba a mfiase no ɛne adwene bɔ abira efisɛ dade mu yɛ duru sen magnesium.

Ɛsono sɛnea ɔhyew nya nhyehyɛe no so nkɛntɛnso. Ɔhyew ma unit cell no trɛw, a b-axis no kyerɛ ɔhyew ntrɛwmu nsusuwii kɛse. Nhwehwɛmu a ɛfa ɔhyew a ɛkorɔn-wɔ forsterite a ɛkɔ soro kodu digrii 900 so no kyerɛ sɛ M-O nkitahodi tenten no kɔ soro wɔ nhyehyɛe kwan so, nanso mfitiase nhyehyɛe topology no nsakra kosi sɛ ɔhyew a ɛbɔ no bɛn.

SiO4 tetrahedra no da adi sɛ ɛyɛ den ma ɛyɛ nwonwa sɛ wɔde toto dade-oxygen octahedra no ho a. Si-O nkitahodi tenten sesa kakraa bi wɔ nhyɛso anaa ɔhyew mu esiane Si-O nkitahodi ahorow no covalent su a emu yɛ den nti. Nsiesiei mu nsakrae dodow no ara fi nsakrae a wɔyɛ wɔ M-O bond tenten ne anim a ɛda polyhedra ntam sen sɛ wɔbɛhyɛ polyhedra no ankasa mu.

Olivine structure framework no nya mfiridwuma mu dwumadie a ɛho hia wɔlithium dade phosphate batere ahorow(LiFePO4 anaa LFP). Wohuu lithium iron phosphate sɛ cathode ade wɔ 1996 mu, na ɛfa olivine nhyehyɛe titiriw koro no ara te sɛ mineral olivine, ɛwom sɛ phosphate akuw besi silicate tetrahedra a wɔatew wɔn ho no ananmu de.

Wɔ LiFePO4 mu no, nhyehyɛe no kura orthorhombic symmetry (ahunmu kuw Pnma/Pbnm) a lattice parameters a=6.008 Å, b=10.334 Å, ne c=4.693 Å. Dade atɔm di mmeae a ɛwɔ afã awotwe (ɛyɛ FeO7 octahedra), bere a phosphorus atɔm te mmeae a ɛwɔ afã anan (ɛyɛ PO4 tetrahedra), a ɛne sɛnea dade ne silicon atɔm hyehyɛ wɔ mineral olivine mu no di nsɛ.

Nsonsonoe titiriw no wɔ lithium cations a wɔde ka ho no mu. Lithium ions te octahedral akwan a ɛwɔ ɔdan no mu, a wɔahyehyɛ no wɔ zigzag kwan so. Bere a wɔrebɔ batere no na wɔreyi afi mu no, wobetumi asan ayi lithium ions afi saa akwan yi mu na wɔde ahyɛ mu a wɔrensɛe olivine nhyehyɛe titiriw no. Dade no fa redox cycling mu wɔ Fe2+ ne Fe3+ ntam na ama charge kari pɛ bere a lithium kɔ mu na efi mu ba no.

Saa nhyehyeɛ a ɛgyina pintinn-a wonya firii olivine nhyehyeɛ a ɛyɛ den no mu-ma LiFePO4 batere ahobanbɔ su soronko ne kyinhyia nkwa tenten. P-O covalent nkitahodi a emu yɛ den a ɛwɔ phosphate tetrahedra no mu no ko tia oxygen a wɔayi no adi, na esiw ɔhyew guankɔbea nneyɛe a ɛhaw lithium-ion batere nnuru afoforo bi no ano. LFP batere a wɔtɔn no tumi nya charge-discharge cycles bɛboro 3,000 bere a ɛkura tumi mu.

Olivine nhyehyeɛ no de anohyetoɔ baako to hɔ ampa: ɛsɛ sɛ lithium ions trɛw fa akwan baako-afã bi so wɔ crystallographic axes no so sen sɛ ɛbɛkɔ ahofadie mu wɔ afã mmiɛnsa. Eyi siw ionic conductivity ne rate tumi ano hye. Nhwehwɛmufo nam nanostructuring (a wɔtew nneɛma nketenkete no kɛse so na ama akwan a wɔfa so trɛw no ayɛ tiaa) ne carbon coating (a ɛma ɛlɛtrɔnik ahoɔden a ɛkɔ mu no tu mpɔn) so di eyi ho dwuma. Nkyerɛase ahorow a wɔayɛ mu nsakrae te sɛ lithium manganese iron phosphate (LMFP) kura olivine nhyehyɛe no mu bere a wɔde manganese si dade bi ananmu de ma adwumayɛ mu ahoɔden kɔ soro no.

Nnɛyi ntease a ɛfa olivine nhyehyɛe ho no fi X-ray diffraction akwan titiriw mu. William Lawrence Bragg ne G. B. Brown dii kan de X-ray ahwehwɛ ho akwan a edi kan dii dwuma de kyerɛɛ forsterite ahwehwɛ nhyehyɛe wɔ afe 1926 mu. Wɔn adwuma no de olivine sii hɔ sɛ ɛyɛ SiO4 tetrahedra a wɔatew wɔn ho-a ɛyɛ fapem nhumu ma silicate mineralogy.

Single-crystal X-ray diffraction da so ara yɛ sika kɔkɔɔ gyinapɛn a wɔde kyerɛ nhyehyɛe pɔtee. Wɔde olivine ahwehwɛ ketewaa bi (a mpɛn pii no ɛyɛ 0.1-0.5 mm) si goniometer so na wɔdannan no fa X-ray hann mu. Diffraction nhyehyɛe a efi mu ba no kura ankorankoro reflections mpempem pii, a emu biara gyina hɔ ma crystallographic planes ahorow a ɛsono emu biara. Software a ɛyɛ nwonwa siesie atom gyinabea, ɔhyew parameters, ne beae a nnipa te ma ɛne diffraction ahoɔden a wɔahu no hyia.

Neutron diffraction ma nsɛm a ɛka ho, a ɛsom bo titiriw ma hydrogen atom ahorow (wɔ nsu mu) ne nsonsonoe a ɛda nneɛma a ɛwɔ electron dodow a ɛte sɛ magnesium ne aluminium ntam. Neutron sɔhwɛ ahorow hwehwɛ sɛ wɔde ahwehwɛ akɛse ne mmeae titiriw a neutron fibea ahorow wom, nanso ɛma wonya pɛpɛɛpɛyɛ a ɛkorɔn a wɔde kyerɛ magnetic nhyehyɛe ne hann element ahorow bi gyinabea.

Transmission electron microscopy (TEM) hwehwɛ olivine nhyehyɛe mu wɔ nanoscale so, na ɛda sintɔ ahorow, domain hye, ne mpɔtam hɔ nsakrae a wontumi nhu wɔ diffraction akwan horow so adi. High-resolution TEM tumi yɛ atom adum ankorankoro ho mfonini, na ɛyɛ atɔm nhyehyɛe ho mfonini tẽẽ. Eyi bɛyɛ nea tumi wom titiriw bere a wɔresua nhwɛsode ahorow a asɛe anaasɛ fase nsakrae a ɛwɔ baabi a nhyehyɛe no gu ahorow wɔ akwansin nketewa so no.

Raman ne infrared spectroscopy hwehwɛ olivine nhyehyɛe mu denam wosow akwan so. SiO4 tetrahedron no wɔ wosow akwan titiriw anan, na wɔn mpɛn dodow gyina Si-O nkitahodi ahoɔden ne nhyehyɛe a atwa ho ahyia no so. Nneɛma a wɔahyehyɛ no nya saa wosow mpɛn dodow yi so nkɛntɛnso wɔ akwan a wotumi hyɛ ho nkɔm so-forsterite kyerɛ spectral peaks soronko sen fayalite efisɛ Fe-O nkitahodi yɛ mmerɛw sen Mg-O nkitahodi. Saa spectroscopic akwan yi yɛ adwuma a ɛnyɛ-ɔsɛeɛ na ɛtumi kyerɛ nhwɛsoɔ nketenkete anaa nea ɛka ho no su.

Crystallographic nhyehyɛe no di olivine su ahorow a wotumi hu no so tẽẽ. Mineral no taa da adi sɛ ngodua-ahabammono efisɛ Fe2+ ions a ɛwɔ octahedral coordination mu no twetwe hann wɔ asorɔkye tenten pɔtee bi mu, na ɛde ahabammono kɔ. Forsterite kronkron no nni kɔla kosi kɔkɔɔ a ɛyɛ mmerɛw-ahabammono, bere a dade-nneɛma a ɛwɔ mu no da adi sɛ ɛyɛ ahabammono tuntum kosi bruu-tuntum.

Olivine da conchoidal fracture adi sen sɛ ɛbɛpaapae efisɛ tetrahedra a atew ne ho a ɛbata octahedra ho no afã abiɛsa-frafrae no ma nkitahodi a emu yɛ den pɛpɛɛpɛ wɔ akwan nyinaa so. Mmerewa nhyehyɛe biara nni nhyehyɛe no mu a wɔde toto nkratafa nhyehyɛe a ɛwɔ micas anaa layer silicates mu no ho. Sɛ olivine bubu a, ɛpaapae wɔ ɔkwan a ɛnteɛ so wɔ ɔdan no mu sen sɛ ɛbɛpaapae wɔ ahwehwɛ nhyehyɛe pɔtee bi so.

Orthorhombic symmetry no ma anisotropic su ahorow-honam fam su ahorow gu ahorow wɔ crystallographic akwankyerɛ mu. Ɛsono sɛnea asasewosow asorɔkye ahoɔhare kɔ no gyina sɛnea ɛtrɛw no so bere a wɔde toto ahwehwɛ no agyan no ho. Ahoɔhare a ɛkɔ ntɛmntɛm no kwankyerɛ no ne a-axis no hyia, ahoɔhare a ɛwɔ mfinimfini no ne c-axis no hyia, na ahoɔhare a ɛkɔ brɛoo no ne b-axis no hyia. Saa asasewosow anisotropy a ɛwɔ mantle olivine mu yi boa asase ho animdefo ma wɔkyerɛ kwan a mantle no sen ne ne kɛse ase.

Hardness (6.5-7 wɔ Mohs nsenia so) ne density (3.27-3.37 g/cm3 ma forsterite, 4.39 g/cm3 ma fayalite) nyinaa fa sɛnea wɔde ahyɛ ɔdan no mu denneennen ne ahoɔden a ɛwɔ dade-oxygen nkitahodi mu ho. Oxygen nhyehyɛe a ɛyɛ den ne dade ne oxygen ntam kwan tiaa a ɛwɔ olivine nhyehyɛe no mu no ma aboɔden abo a ɛyɛ den na ɛyɛ den a nnuru ntumi nsɛe no wɔ Asase tebea a emu dɔ mu.

olivine crystal structure

Olivine ahwehwɛ ankasa wɔ nhyehyɛe mu sintɔ ahorow a ɛka wɔn nneyɛe kɛse. Point sintɔ ahorow no bi ne vacancies (atom ahorow a enni hɔ), interstitials (atom afoforo a wɔapiapia akɔ mmeae a mpɛn pii no obiara nni hɔ), ne substitutional defects (atom ahorow a ɛnteɛ wɔ mmeae a ɛfata). Ɛwom sɛ saa sintɔ ahorow yi ntaa mma de, nanso ɛhwɛ sɛnea ɛtrɛw ne anyinam ahoɔden a ɛkɔ mu no so denam akwan a ɛma ionic fa so tu no so.

Dislocations-line defects a ɛwɔ baabi a daa crystallographic nhyehyɛe no sɛe-di olivine mfiridwuma su so. Dislocation creep (saa line defects yi fa crystal no mu) gyina hɔ ma deformation mechanism titiriw wɔ mantle olivine mu wɔ geological bere nhyehyɛe ase. Slip nhyehyɛe pɔtee (crystallographic planes ne dislocation motion akwankyerɛ) na ɛkyerɛ sɛnea olivine aburow no sesa na ɛma crystallographic orientations a wɔpɛ.

Mfomso a ɛtrɛw te sɛ aburow ahye ne twin hye ma nkitahodi ahorow a ahwehwɛ nhyehyɛe no dan fi ɔkwan biako so kɔ foforo so. Saa ahye yi nya mfiri ahoɔden so nkɛntɛnso na ɛma akwan a ɛtrɛw ntɛmntɛm ma nnuru sesa. Subgrain hye-low-angle hye a wɔahyehyɛ no arrays of dislocations-nya nkɔso wɔ deformed olivine mu na kyerɛw deformation abakɔsɛm.

Wɔ Asase ani no, olivine tumi sesa ntɛmntɛm ɛmfa ho sɛ ɛyɛ den no. Nsu mu nneɛma nketenkete tumi fa sintɔ ne aburow ahye so, na ɛne olivine nhyehyɛe no yɛ adwuma. Nsakraeɛ a ɛtaa ba ne serpentine, a ɛba berɛ a nsuo molecules hyɛ nhyehyɛeɛ no mu: 2Mg2SiO4 + 3H2O → Mg3Si2O5(OH)4 + Mg(OH)2. Saa adeyɛ yi trɛw mfitiase dodow no mu 30-40% na ɛsɛe mfitiase olivine nhyehyɛe no, na ɛde sheet silicate layers si ananmu.

Nneɛma afoforo a wɔde yɛ nsakrae no bi ne iddingsite (dade oxides ne dɔte mu nneɛma a wɔde afrafra a ɛyɛ fɛ-grained) ne bowlingite (hydrated iron-a ɛwɔ silicates). Saa nsakrae ahorow yi kɔ so ntɛmntɛm sen biara wɔ mpaapaemu ne ahwehwɛ anoano baabi a nsu betumi akɔ ɔdan no mu ntɛm ara. Pseudomorphic replacement koraa betumi aba, baabi a nneɛma a wɔasesa no kura abɔnten so ahwehwɛ nsusuwii bere a emu nhyehyɛe no dan koraa yɛ aboɔden abo a ɛto so abien.

Dɛn na ɛma olivine nhyehyɛe yɛ soronko wɔ silicate mineral afoforo ho?

Olivine kura SiO4 tetrahedra a atew ne ho a ɛnkyɛ oxygen atom ne wɔn ho wɔn ho, na ɛkyerɛkyerɛ mu sɛ nesosilicate. Eyi ne nkɔnsɔnkɔnsɔn silicates (te sɛ pyroxenes), sheet silicates (te sɛ micas), ne framework silicates (te sɛ quartz) a tetrahedra kyɛ oxygen ahorow ma ɛyɛ nhyehyɛe a ɛtrɛw no bɔ abira. Tetrahedra a atew ne ho no yɛ ntama a ɛyɛ den a ɛwɔ afã abiɛsa-a dade-oxygen nkitahodi ahorow kura mu.

Dɛn nti na olivine wɔ dade mmeae ahorow abien (M1 ne M2)?

Orthorhombic symmetry ne oxygen atɔm ahorow no packing nhyehyɛe pɔtee no ma octahedral gyinabea abien a ɛsono emu biara wɔ crystallographically a ɛsono ne kɛse ne ne distortions kakra. M1 te inversion center so na ɛyɛ ketewaa na ɛyɛ kyinkyim kɛse, bere a M2 da ahwehwɛ wimhyɛn so na ɛyɛ kɛse na ɛyɛ daa. Saa nsonsonoe yi ka cations bɛn na wɔpɛ mmeae bɛn na ɛhwɛ ade no honam fam su so.

Ɔkwan bɛn so na nneɛma a wɔahyehyɛ no nya olivine ahwehwɛ nhyehyɛe so nkɛntɛnso?

Sɛnea dade si magnesium ananmu wɔ forsterite-fayalite ntoatoaso no nyinaa mu no, unit cell no trɛw pɛpɛɛpɛ efisɛ Fe2+ sõ sen Mg2+. Mfitiaseɛ nhyehyeɛ topology no da so ara nsakra-ahunmu kuo korɔ no ara, atom gyinabea korɔ no ara, nkitahodiɛ atwa yɛn ho ahyia korɔ no ara. Bond tenten kɔ soro kakra, nanso atɔm nhyehyɛe no kɔ so yɛ pɛ titiriw. Wei ma kwan ma ano aduru a ɛyɛ den a edi mũ wɔ awiei-asɔremma no ntam.

So olivine nhyehyɛe betumi afa nsu anaa nneɛma afoforo a ɛyɛ hyew?

Standard olivine nhyehyɛe no nni hydroxyl akuw anaa molecule nsu biara. Nanso, hydrogen kakraa bi betumi de ahyɛ mu sɛ nsɛntitiriw sintɔ-mpɛn pii no sɛ OH akuw a wɔde si oxygen atɔm ananmu anaasɛ wɔte mmeae a mpɛn pii no ɛda mpan. Saa "nsu" a ɛwɔ mu yi da so ara sua koraa (mpɛn pii no<50 ppm by weight), but even trace hydrogen significantly affects electrical conductivity and diffusion rates. Water content increases with pressure, making transition zone olivine polymorphs potentially important water reservoirs in Earth's deep interior.

Olivine ahwehwɛ nhyehyɛe no da su atitiriw a edidi so yi adi:

Crystal Nhyehyɛe: Orthorhombic a ahunmu kuw Pbnm (anaasɛ Pnma wɔ tebea foforo mu) .

Lattice Nneɛma a Wɔde Yɛ Nneɛma:

Forsterite: a ≈ 4.75 Å, b ≈ 10.20 Å, c ≈ 5.98 Å

Fayalite: a ≈ 4.82 Å, b ≈ 10.48 Å, c ≈ 6.09 Å

Nneɛma a Wɔde Sisi Adan: SiO4 tetrahedra a wɔatew ho a ɛnam dade-oxygen octahedra (MO3) so na ɛka bom .

Nneɛma a Wɔde Dade Yɛ: Mmeae abien a ɛsono emu biara a ɛwɔ octahedral (M1 ne M2) a ɛsono ne kɛse ne ne kyinkyim

Oxygen Gyinabea Ahorow: Oxygen mmeae abiɛsa a ɛsono wɔ ahwehwɛ mu wɔ asymmetric unit no mu

Nhyehyɛe a Wɔde Yɛ Adwuma: Hexagonal close-packed oxygen array a cations wɔ tetrahedral ne octahedral voids mu

Nkyekyɛmu a wɔkyekyɛ mu: Nesosilicate (orthosilicate) esiane tetrahedral akuw a wɔatew wɔn ho nti

Nkitahodi a wɔyɛ: Si wɔ 4-nhyehyɛe (tetrahedral), M cations wɔ 6-nhyiam (octahedral) mu .

Saa nhyehyeɛ yi da ne ho adi sɛ ɛyɛ den ma ɛyɛ nwonwa, ɛma ɛyɛ den wɔ nneɛma a wɔahyehyɛ no ahodoɔ pii mu wɔ asase ho nneɛma a atwa yɛn ho ahyia mu berɛ a ɛsan nso ma fapem ma batere nneɛma a ɛkɔ anim wɔ mfiridwuma mu dwumadie mu. Olivine nhyehyɛe no a ɛka bom yɛ covalent Si-O nkitahodi a emu yɛ den ne dade a ɛyɛ mmerɛw-oxygen nkitahodi ma ɛyɛ Asase so aboɔden abo nhyehyɛe a ɛho hia sen biara na ɛyɛ adwuma pii no mu biako.