Mineral magnetic properties of artificial samples systematically mixed from haematite and magnetite

Abstract

S U M M A R YDetailed rock magnetic investigations were carried out on a set of samples with defined ratios of haematite and magnetite. The measured parameters provide a reference for interpreting common rock magnetic parameters in investigations of sediments. The contribution of haematite to the magnetic fraction must exceed 95 wt-% of the magnetic fraction when mixed with magnetite in order to visibly influence grain size and coercitivity indicative magnetic parameters. Coercivity of remanence (B CR ) and coercive force (B C ) do not change in the same way with increasing haematite content, which results in a peak B CR /B C value at around 99.5 wt-% haematite. Variations in haematite content can be ignored when interpreting most rock magnetic parameters, especially grain size indicative parameters for samples where haematite contents range from 0 to 98 wt-%. The S-ratio is still the most sensitive parameter for estimating the relative amount of haematite in magnetite/haematite mixtures. A combination of S-ratio, the saturation isothermal remanent magnetization divided by the low field magnetic susceptibility (SIRM/κ LF ) and B CR is the most effective way to identify haematite in natural samples . Our results agree with literature data and fill the gap between results obtained either from pure magnetite or haematite with comparable grain sizes.

A New Tool for Separating the Magnetic Mineralogy of Complex Mineral Assemblages from Low Temperature Magnetic Behavior

“…Furthermore, for remanence data, fine particles smaller than the superparamagnetic to stable single domain grain size boundary at room temperature will also go undetected. Induced magnetization data is inclusive of all minerals but differences over three orders of magnitude in saturation magnetizations heavily biases hysteresis loop derived data toward strongly ferrimagnetic minerals (e.g., magnetite, see for instance Frank and Nowaczyk, 2008). Decomposing induced magnetization data requires a priori knowledge of basis functions of the individual components (Carter-Stiglitz et al, 2001).…”

Magnetic Properties of Cherts from the Basque-Cantabrian Basin and Surrounding Regions: Archeological Implications

“…This indicates that magnetite is the main magnetic mineral, with some likely contribution from hematite (Thompson and Oldfield, 1986;Verosub and Roberts, 1995;Frank and Nowaczyk, 2008). The rest of the samples have S ratios down to 0.1, which points to either the dominance of hematite (Frank and Nowaczyk, 2008) or the additional occurrence of goethite (Thompson and Oldfield, 1986;Bloemendal et al, 1992;Verosub and Roberts, 1995). Keeping in mind that our measurements were conducted with fresh chert samples, and therefore avoiding present-day weathering, we interpret that magnetic minerals in the studied BCB chert types represent primary constituents that have been enclosed in chert during early diagenetic replacement of the parent sediment by silica within concretions.…”

Keuper magnetostratigraphy in the southern Mesozoic margin of the Holy Cross Mts. (southeastern edge of the German Basin)

“…On the con trary, the ex am ple il lus trated in Fig ure 5B char acter izes a rapid in crease of mag ne ti za tion be tween 0 and 0.2 T, unachieved sat u ra tion, rapid de crease of MS be tween 450 and 500°C, in crease of MS be tween 650 and 700°C, and complete re moval of IRM at ~700°C. The in crease of mag ne ti zation can be in ter preted as a re sult of ad mix ture of mag ne tite in the sam ple dom i nated by haematite, like in the Mid dle Tri as sic from the Ibe rian Ranges (Rey et al, 1996) and in the Buntsandstein de pos its from the Ger man Ba sin (Szurlies, 2004(Szurlies, , 2007; see also ex per i ments with mix ture of haematite and mag ne tite pro vided by Frank and Nowaczyk, 2008). The pres ence of low-coercivity min eral can be clearly in ter preted from the three-axes ther mal de mag ne ti za tion curves (Fig.…”