The compositions of rocks and soils on Mars shown here have been superseded by the results presented in: Rieder, R., et al., 1997, The chemical composition of the Martian soil and rocks returned by the mobile Alpha Proton X-ray Spectrometer: Preliminary results from the X-ray mode, Science, 278: 1771-1774.

Mars Pathfinder

Analysis of Martian Samples by the Alpha Proton X-Ray Spectrometer: Preliminary Results
Elements

Element	A-2, Soil	A-4, Soil	A-5, Soil	A-3, Rock "Barnacle Bill"	A-7, Rock "Yogi"
	weight %	weight %	weight %	weight %	weight %
Carbon [C] (see note 2)	-	-	-	-	-
Oxygen [O] (see note 2)	42.5	43.9	43.2	45.0	44.6
Sodium [Na]	3.2	3.8	2.6	3.1	1.9
Magnesium [Mg]	5.3	5.5	5.2	1.9	3.8
Aluminum [Al]	4.2	5.5	5.4	6.6	6.0
Silicon [Si]	21.6	20.2	20.5	25.7	23.8
Phosphorus [P]	-	1.5	1.0	0.9	0.9
Sulphur [S]	1.7	2.5	2.2	0.9	1.7
Chlorine [Cl]	-	0.6	0.6	0.5	0.6
Potassium [K] (see note 4)	0.5	0.6	0.6	1.2	0.9
Calcium [Ca]	4.5	3.4	3.8	3.3	4.2
Titanium [Ti]	0.6	0.7	0.4	0.4	0.5
Chromium [Cr]	0.2	0.3	0.3	0.1	0.0
Manganese [Mn] (see note 4)	0.4	0.4	0.5	0.7	0.4
Iron [Fe]	15.2	11.2	13.6	9.9	10.7
Nickel [Ni]	-	-	0.1	-	-
Sum	100.0	100.0	100.0	100.0	100.0

Notes:

1. Analysis based on X-ray data.
2. Direct results on carbon and oxygen will be available from the analysis of the alpha spectra at a later date.
3. Oxygen is calculated from oxide stoichiometry, assuming sulphur in the form of SO3 and iron in the form of FeO.
4. Values for potassium and manganese are upper limits; more accurate numbers will be available after further analysis.

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