Feldspar Earth's Crust Abundance

The first statement concerns the abundance of feldspar in the Earth's crust. Feldspar is indeed a highly abundant mineral group. It constitutes a major part of the Earth's crust, often cited as making up around 40-41% of the crust by weight. While technically not exactly half, this significant proportion makes the statement generally acceptable in many contexts, especially when contrasting with other mineral groups.

Feldspar Colour Characteristics

The second statement addresses the colour of feldspar. Feldspars are known for their diverse colour palette, which can include white, grey, pink, red, brown, green, and even blue or violet hues, depending on their specific type and impurities. Light cream to salmon pink colours are particularly common, often associated with alkali feldspars like orthoclase and microcline. Therefore, this statement accurately describes common feldspar colours.

Feldspar Elemental Composition

The third statement focuses on the elemental composition of feldspar, specifically mentioning magnesium. Feldspars belong to the tectosilicate group and are primarily composed of silicon (Si), aluminium (Al), oxygen (O), and either potassium (K), sodium (Na), or calcium (Ca). Common elements include silicon, aluminium, potassium, sodium, and calcium. Magnesium (Mg) is not a defining or common constituent element found across all types of feldspar. Minerals like olivine or pyroxene are typically rich in magnesium. Hence, this statement is incorrect.

Summary of Feldspar Statements

• Statement 1: Feldspar comprises a significant portion (around 41%) of the Earth's crust. This is considered correct.
• Statement 2: Feldspar commonly exhibits colours ranging from light cream to salmon pink. This is correct.
• Statement 3: Magnesium is a common element in all feldspars. This is incorrect.

Based on the analysis, statements 1 and 2 are correct, while statement 3 is incorrect.