School of GeoSciences

School of GeoSciences

Tephra Standards

It is essential that any Tepra analysis from any EPMA laboratory is presented together with a recognised standard and the analytical conditions. The NERC Tephrochronology unit uses a Lipari obsidian (Hunt and Hill, 1996 Quarternary International V34-36 pp 229-241) as an indication of the quality of the analyses acquired.

The table below shows the the variation in the analysis of the same Tephra sample from 9 EPMA labs/insturments together with the 'accepted' XRF and wet chemical analysis.

  SiO2 Na2O K2O FeO* MgO Al2O3 CaO MnO SUM
EPMA Edinburgh (WDS)                  
min. 73.90 3.73 4.99 1.18 0.02 12.70 0.69 0.00 97.21
max. 74.82 4.07 5.48 1.65 0.08 13.03 0.79 0.70 100.62
mean (20) 74.35 3.93 5.12 1.51 0.05 12.87 0.74 0.08 98.65
2 Sigma 0.34 0.12 0.10 0.10 0.02 0.12 0.04 0.10  
                   
EPMA Edinburgh (WDS)                  
min. 73.85 3.89 5.02 1.34 0.03 12.69 0.71 0.02 97.55
max. 74.85 4.27 5.31 1.64 0.08 13.33 0.81 0.11 100.4
mean (20) 74.27 4.07 5.17 1.49 0.05 13.00 0.74 0.07 98.86
2 Sigma 0.60 0.20 0.16 0.16 0.12 0.28 0.06 0.04  
                   
EPMA Lab.3 (WDS)                  
min. 74.16 2.48 4.79 1.39 0.00 13.14 0.62 0.00 96.58
max. 76.96 3.02 5.49 1.71 0.46 13.91 0.88 0.24 102.67
mean (20) 75.58 2.78 5.20 1.54 0.03 13.53 0.75 0.09 99.5
2 Sigma 1.56 0.34 1.22 0.14 0.16 0.36 0.14 0.14  
                   
EPMA Lab.4 (EDS)                  
min. 59.04 9.86 3.19 0.57 0.00 11.79 0.29 0.00 84.74
max. 68.25 22.19 5.86 2.17 0.23 13.76 1.41 0.25 114.12
mean (20) 63.02 17.56 4.24 1.23 0.07 12.74 0.61 0.05 99.52
2 Sigma 4.28 6.20 1.22 0.82 0.16 1.00 0.38 0.16  
                   
EPMA Lab.5 (WDS)                  
min. 72.53 3.99 2.47 0.81   11.95 0.65   92.4
max. 74.80 5.95 5.72 1.69   12.80 1.85   102.81
mean (6) 73.81 4.95 3.88 1.42   12.50 0.92   97.48
2 Sigma 1.82 1.80 2.72 0.64   0.72 0.92    
                   
EPMA Lab.6 (EDS)                  
min. 72.61 3.25 5.14 1.52 0.34 12.67 0.66   96.19
max. 74.03 4.40 5.41 1.73 3.25 13.16 0.79   102.77
mean (15) 73.35 3.92 5.26 1.61 1.25 12.89 0.73   99.01
2 Sigma 0.76 0.72 0.14 0.12 0.16 0.28 0.06    
                   
EPMA Lab.7 (WDS)                  
value (1) 74.90 4.43 4.61 1.51 0.04 13.70 0.72 0.07 99.98
                   
EPMA Lab.8 (WDS)                  
min. 63.08 0.25 2.82 0.34 11.02 0.01     77.52
max. 74.38 3.26 5.52 3.25 13.72 0.52     100.65
mean (20) 69.40 1.54 4.56 1.25 12.66 0.20     89.61
2 Sigma 6.66 2.12 1.44 0.98 1.04 0.18      
                   
EPMA(Cambridge: Dr C Hayward)                  
min. 73.43 4.04 5.26 1.49 0.04 12.76 0.75 0.04 98.00
max. 74.83 4.26 5.49 1.57 0.05 13.10 0.76 0.09 99.59
mean (10) 74.11 4.15 5.36 1.52 0.05 12.94 0.76 0.07 98.94
2 Sigma 0.34 0.07 0.08 0.02 0.00 0.10 0.01 0.02 0.44
                   
XRF Edinburgh                  
value 73.72 4.06 5.06 1.75 0.03 13.04 0.76 0.06 98.48
                   
XRF Lab. 10                   
Value 74.03 4.06 5.18 1.73 0.00 12.72 0.72 0.08 98.52
                   
Wet chem 1.                  
min.   3.78 4.50            
max.   4.34 5.33            
mean   4.06 4.99            
2 Sigma   0.15 0.25            
                   
Wet chem.  2.                  
min.   3.55 4.86            
max.   4.12 5.19            
mean   3.89 5.01            
2 Sigma   0.17 0.13