Question

Evaluate the following statements about elements and minerals: Which of the options is correct?

1. Some elements like Gold and Silver can be found in their pure 'native' form without combining with others.
2. Sodium and Potassium together contribute more than 5% of the Earth's crust by weight.
3. 'Specific Gravity' is the same as the 'Streak' of a mineral.

• A. All
• B. i only
• C. None of these
• D. iii only

Answer 1

Answer:

B. i only

• Native Elements: Certain elements, such as Gold (Au), Silver (Ag), Copper (Cu), Platinum (Pt), and Sulfur (S), occur naturally in their elemental form, uncombined with other elements. These are referred to as native elements. This native state is possible when the element is relatively unreactive chemically.
• Abundance in Earth's Crust: Sodium (Na) constitutes about 2.6% and Potassium (K) about 2.4% of the Earth's crust by weight. While both are abundant, their combined contribution is approximately 5%, but it's important to note they are typically found in compounds (minerals) rather than their native form. For example, sodium is commonly found in halite (NaCl) and potassium in feldspars.
• Mineral Properties:
  Specific Gravity (or Relative Density) is the ratio of the density of a mineral to the density of a reference substance (usually water). It's a measure of how heavy a mineral is for its size. For example, Galena (PbS) has a high specific gravity of about 7.5.
  Streak, on the other hand, is the color of a mineral in its powdered form, which is determined by rubbing the mineral against an unglazed porcelain plate. The streak color can be different from the mineral's external color and is a more reliable identification property. For instance, Hematite (Fe2O3) can appear black or reddish-brown externally, but its streak is always reddish-brown.