NAME MINERALOGY AND OPTICAL CRYSTALLOGRAPHY FORENSIC APPLICATIONS OF X-RAY DIFFRACTION. λ ' 2d sinθ -1- I. Introduction

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NAME 89.301 - MINERALOGY AND OPTICAL CRYSTALLOGRAPHY FORENSIC APPLICATIONS OF X-RAY DIFFRACTION I.

1 NAME MINERALOGY AND OPTICAL CRYSTALLOGRAPHY FORENSIC APPLICATIONS OF X-RAY DIFFRACTION I. Intrductin Our knwledge f the crystalline state is gained by studies utilizing x-rays (the field f x- ray crystallgraphy). Let us suppse that a beam f mnchrmatic x-rays is incident n a crystal (Fig. 1). If the wavelength f the x-rays is similar t that f the spacing between the planes f atms (fr example, let us assume we are using Cu K radiatin fr which λ = 1.54 Å, an α -10 Å = 1 x 10 m, a very small unit f distance) the x-rays will be scattered by the atms. Fr certain incident angles and spacings between the planes f atms cnstructive interference will ccur and a diffracted beam will leave the crystal at an angle equal t that f the incident beam. The relatinship between x-ray wavelength, angle f incidence and spacing between planes f atms is knwn as Bragg s Law. λ ' 2d sinθ Fig. 1. Interactin between x-rays and the crystal structure. Where λ is the x-ray wavelength, d is the spacing between planes f atms, and θ is the incident angle. While a very simple equatin, this relatinship represents a pwerful way t investigate the structure f crystalline materials. X-ray data fr crystalline materials is ften acquired using x-ray pwder diffractrmetry (Fig. 2). An x-ray tube prvides a mnchrmatic x-ray beam. Thus, the wavelength is knwn. The sample is in a fixed gemetry, usually pwder n a glass slide, and a sensr is scanned thrugh a 2θ angle (Fig. 3). When cnstructive interference ccurs a diffracted beam is sent t the sensr giving the 2θ angle. The remaining unknwn is the d spacing. Fr any particular mineral there are multiple paths with different d spacings, and each f these will be recrded. In additin, fr a mineral that cnsists f mre than ne element, the areal distributin f the different elements will vary as a functin f the plane that is diffracting the x-ray beam. Since different atms interact differently with the x-ray beam, the intensity f the diffracted signal varies as a functin f the particular atmic plane that is respnsible fr the diffracted beam. Thus, we btain a secnd imprtant piece f infrmatin, the intensity f the diffracted x-ray beam, which can be related t the cmpsitin f the crystalline slid. Tens f thusands f crystalline cmpunds have been characterized by x-ray diffractin. Taking int accunt the d-spacing and relative intensities f the diffracted beam virtually every crystalline cmpund has a unique x-ray fingerprint. This infrmatin is available in the American Sciety fr Testing and Materials Pwder Data File which is frequently updated and cntains infrmatin fr -1-

$Figure 2. X-ray diffractmeter. all knwn crystalline materials. Thus, we have a pwerful methd fr identifying crystalline slids even if individual particles are very small. d ' λ 2sinθ d ' 1.$ $In the fllwing prblems we will be using a cpper (Cu) x-ray tube in which case Bragg s law is Nte that the diffractin angle is measured as 2θ. In the equatin abve we use the θ angle.$

2 Figure 2. X-ray diffractmeter. all knwn crystalline materials. Thus, we have a pwerful methd fr identifying crystalline slids even if individual particles are very small. d ' λ 2sinθ d ' 1.54Å 2sinθ Figure 3. Clse-up view f x-ray tube, sensr, and sample (pwder n glass slide). 2θ is the angle between the x-ray tube and the sensr. What we usually measure is the 2θ angle frm which we can calculate the d spacing by slving Bragg s equatin fr d. In the fllwing prblems we will be using a cpper (Cu) x-ray tube in which case Bragg s law is Nte that the diffractin angle is measured as 2θ. In the equatin abve we use the θ angle. Hence, the 2θ angle must be divided by 2 t get the θ angle used in the equatin. Fr example, if the 2θ angle is 32, the θ angle is 16. Reference x-ray diffractin patterns fr a number f crystalline slids are attached t this exercise. These data are t be used in answering (slving) the fllwing prblems and cases. Fr the unknwn XRD patterns nly the three mst intense peaks are shwn fr each crystalline slid in the unknwn. II. Csmetics Varius minerals are used in csmetics t prvide clr and texture. In this exercise we will lk at several types f lipsticks fr which we have x-ray diffractin data. X-ray diffractin data fr 4 lipsticks are shwn belw. -2-

3 Figure 4. XRD pattern fr Trpez A. Figure 5. XRD pattern fr Trpez B. Figure 6. XRD pattern fr Avn Red K. Figure 7. XRD pattern fr Cver Girl Classic Red 1. Fr Trpez A (Fig. 4) list the 2 theta angle, relative intensity, and d-spacing fr each peak. 2θ I/I d (Å) 2. Des Trpez A (Fig. 4) cntain either chlrite r kalinite. Hw did yu make this determinatin? -3-

4 3. By lking at the 3 largest peaks in Trpez B (Fig. 5) and Cver Girl Classic Red (Fig. 7), d these lipsticks cntain the same minerals r are they different mineral assemblages? 4. D Avn Red K and Cver Girl Classic Red cntain any minerals in cmmn? If they cntain mineral(s) in cmmn, what rle might these mineral(s) play in the appearance f the lipsticks? 5. A yung man is murdered, apparently an act f passin. A lipstick smear is fund n his shirt cllar. The man was knwn t be dating tw wmen, and they are ptential suspects. When taken in fr questining Suspect A was wearing Trpez B lipstick and Suspect B was wearing Cver Girl Classic Red lipstick. Bth wmen claimed that it had been at least a week since they saw the victim. The lipstick smear recvered frm the victim s cllar gave the fllwing XRD pattern (Fig. 8). -4-

5 Figure 8. XRD pattern fr lipstick smear recvered frm victim. Frm this evidence, what can yu cnclude abut pssibility f either suspect being the murderer? Explain in detail? -5-

6 III. Pttery and Minerals Minerals are used in pttery fr the clay and glazes. Glazes are applied prir t firing f the pttery and prvide the clratin. Given that any particular type f pttery may cnsist f a relatively unique grup f minerals it is pssible t characterize pttery frm different surces. Pttery clays cnsists f mixtures f the fllwing minerals - bitite, chlrite, kalinite, kyanite, mntmrillnite, pyrphyllite, and quartz. Different mixtures f minerals are used depending n the desired prperties f the resulting pttery (ceramic). Minerals in the glazes are respnsible fr the final clr f the pttery (Table 1). Table 1. Minerals used fr pttery glazes Mineral Frmula Clr Cassiterite SnO2 white Cuprite Cu2O green (xidatin), red (reductin) Esklaite Cr2O3 green Gethite FeO(OH) yellw, tan, brwn Hematite Fe2O3 tan, brwn Ilmenite Fe(Ti,Mg)O3 tans and buffs Pyrlusite MnO2 red, blue, purple, black Rutile TiO2 yellw t tan (xidatin), blue and purple (reductin) Sphaercbaltite CCO3 blue Tenrite CuO green (xidatin), red (reductin) Zincite ZnO brwn 6. A piece f brken pttery is fund at a crime scene. The XRD pattern fr this pttery is shwn n the next page (Fig. 9). Identify the minerals in the pttery. T d this yu need t determine the tw theta values and relative intensities. List the minerals and the pertinent data belw. -6-

7 Figure 9. XRD pattern fr brken pttery fund at crime scene. 7. A piece f brken green pttery is fund at a crime scene. A persn f interest is apprehended and is fund t have small bits f green pttery embedded in his she. The x-ray patterns fr the crime scene (Fig. 10) and the pttery embedded in the she (Fig. 11) are shwn belw. Figure 10. XRD pattern fr brken pttery at crime scene. Figure 11. XRD pattern fr piece f pttery embedded in suspect s she. -7-

8 Identify the minerals in each pttery sample. Are there any differences? Explain. Is the pttery embedded in the suspect s she frm the crime scene? Explain. 8. A nndescript pwder is fund adhering t a suspect s pants leg. The XRD pattern fr this unknwn material is shwn belw (Fig. 12). Figure 12. XRD pattern fr pwder n suspect s pants. -8-

9 Identify the minerals in the pwder. List the minerals and the relevant x-ray data. What is the surce f this pwder? What was the mst likely clr f the bject that was the surce f the pwder? Explain. -9-

10 XRD REFERENCE SPECTRA -10 All spectra are fr Cu-Kα x-rays (λ = 1.54Å). Å = Angstrm, a unit f distance = 1 x 10 m. I/I is the relative intensity. I/I = 100 identifies the diffracted peak with the greatest intensity. The y-axis n each f the images is the relative intensity (I/I ). The line that extends t the tp f the graph represents the peak with the greatest intensity. Using Bragg s Law, fill in the missing values in the tables. The X-ray spectra and data reprted in the fllwing figures and tables are frm the site CLAYS IN POTTERY Bitite Chlrite

11 Kalinite Kyanite Mntmrillnite Pyrphyllite

12 Quartz d I/I θ 2θ POTTERY GLAZES Cassiterite Cuprite

13 Esklaite Gethite Hematite Ilmenite

14 Pyrlusite Rutile Sphaercbaltite Tenrite

15 Zincite d I/I θ 2θ COSMETICS Muscvite is used in sme csmetics t prvide a pearly-like appearance. Other minerals used in mdern csmetics are rutile and hematite fr yellwish and reddish clrs respectively. XRD data fr these tw minerals are fund in the preceding sectin fr Pttery Glazes. Muscvite d I/I θ 2θ

GEOL.3070 EARTH MATERIALS I FORENSIC APPLICATIONS OF X-RAY DIFFRACTION

GEOL.3070 EARTH MATERIALS I FORENSIC APPLICATIONS OF X-RAY DIFFRACTION NAME I. Introduction Our knowledge of the crystalline state is gained by studies utilizing x-rays (the field of x- ray crystallography).