The phrase "a natural sample of" is correct and usable in written English.
It can be used when referring to a specimen or example that occurs in nature, often in scientific or research contexts.
Example: "The researchers collected a natural sample of soil to analyze its composition and nutrient levels."
Alternatives: "a natural specimen of" or "an organic sample of".
Spectra of a natural sample of enstatite (Fig. 4) display a distinct CF at 8.4 µm and a broad Reststrahlen band around 9.3 µm (Salisbury et al. 1991) as well as an additional broad Reststrahlen feature between 12 and 14 µm (that is shifted to longer wavelengths in the spectra of high-Ca pyroxenes).
The intervention group consists of GPs who are willing to participate and the control group is expected to be a natural sample of GPs.
A study of a natural sample of interns in Stockholm found no difference in clinical performance between interns who had been admitted to KI medical school by interview and others [ 15].
The culture used for the reference genome sequence came from a natural sample of O. tauri isolated 1995 in the Thau Lagoon [ 11, 12] and maintained by serial subcultures using 50 ml plastic tissue culture flasks in 20 ml K medium at 20°C under 100 μE s-1 m-2 constant light in Banyuls sur mer.
Third, simultaneously recorded neurons gave a more natural sample of the NPC because these neurons were involved although to different degrees in exactly the same behaviors within a session and across sessions.
To apply the technique to natural samples of various shapes, we developed a method to correct the spectrum of melt inclusion contaminated with host minerals.
Statistical data extracted from natural samples of calcite-cemented microstructures (Kile et al. 2000) follow a lognormal grain size distribution (GSD).
The cathodic reduction of natural samples of high-purity galena has been studied in both acidic and alkaline solutions.
The hydrogen isotope fractionation of our H2-syntrophic dataset overlaps with those obtained not only from low-pH2 experiments reported so far but also from natural samples of "young" methane reservoirs (0.66 0.74).
Figure 7 Isotope compositions (δ18O vs. δ13C) of natural samples of benthic microbial mat and nesquehonite crusts, as well as precipitates from the field microcosm and laboratory precipitation experiments.
