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Proprietati electriceProprietati magneticeRadioactivitatea
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Proprietati electriceConductivitatea electrica este in relatie cu tipul de legaturi din retea:•Mineralele cu legaturi metalice pure (elementele native) sunt excelenti conductori electrici;
•Minerale cu legaturi partial metalice (sulfurile) - semiconductori;
•Minerale cu legaturi ionice si covalente - non-conductive – izolatori
In mineralele non-izometrice conductivitatea electrica este este o proprietate vectoriala.
Proprietati speciale ale unor izolatori:-Piezoelectricitatea-Piroelectricitatea
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Piezoelectricitatea
La aplicarea unei presiuni la capetele axelor polare se se produce polarizare electrica
CUARTTURMALINA
Jacques si Pierre Curie (1881)
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Piezoelectricitatea
Stabilizator de frecventa in computere
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Piroelectricitatea
•Cresterea temperaturii poate determina in cristale incarcare pozitiva si negativa la capetele axelor polare;
•Doar in cristale cu axe polare unice (cuart/turmalina);
•Polarizarea este rezultatul deformarii aparute datorita expansiunii termice inegale (si proprietatile termice sunt vectoriale…)→efect piezoelectric
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Proprietati magnetice
→ fiecare electron poate fi privit ca un magnet punctual;Un orbital trebuie sa cuprinda 2 electroni de spin opus→ moment magnetic zero!
Substantele formate din elemente cu orbitali complet ocupati → diamagneticeex. calcit – CaCO3, albit – NaAlSi3O8, apatit – Ca5(PO4)3(F, Cl, OH)
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Paramagnetism→aranjament neregulat de diopil magnetici
Ferimagnetism – dipoli antiparaleli
Feromagnetism – dipoli paraleli-incalzit peste temp. Curie – se pierde magnetizarea
Aplicatii - paleomagnetism
Aranjament paralel datorat aplicatii unui camp magnetic exterior
Susceptibilitate magnetica scazuta
augit - (Ca, Na)(Mg, Fe, Al)(Al, Si)2O6
olivina (Mg,Fe)2SiO4
Magnetit, hematit, ilmenit, pirotina
Proprietati magnetice
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Concluzie
FeromagnetismParamagnetism Diamagnetism Ferimagnetism
Paleomagnetism remanent
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Cuarț (SiO2)
Calcit (CaCO3)
Grafit (C)
Halit (NaCl)
Sphalerit (ZnS)
Minerale diamagnetice
Hunt et al (1995)
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Minerale paramagnetice
Olivina (Fe,Mg)2SiO4
Siderit (FeCO3) Serpentinit
Chromit (FeCr2O4)
Hunt et al (1995)
Montmorillonit (filosilicat argilos)
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Fier nativ
Minerale feromagnetice
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Ilmenit (
hematit
magnetit
ulvospinel
pirotina
Minerale ferimagnetice
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Radioactivitatea mineralelorNucleii unor elemente sunt instabili si se pot descompune spontan in alte tipuri de nuclei, eliberand energie
Constanta de dezintegrare Rata de dezintegrare in timp a unul nucleu
P – nr. De atomi parentalit- timpλ – constanta de dezintegrare
In timpul descompunerii sunt emise particule alpha, beta si radiatie gamma
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Radioactivitatea mineralelor
Particula alpha Particula beta
n = p + β-
238U→206Pb235U→207Pb232Th→208Pb
Z-2; A-4
p + e- = n
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Autunit Ca(UO2PO4)2 * 10 - 12 H2O
Thorianite ThO2
Uraninit UO2
(pehblenda)
microclin (feldspat), 3 %; muscovit (mica), 2.1%; biotit (mica) 4.1%lepidolite (K, Li-mica) 4.2% ; carnalit, silvina (halogenuri), 0.2%
Minerale radioactive
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Descompunerea minerale radioactive
Metamictizarea