Chapter 7 — Earth Science · Biology. These are 10 questions from the Magmo3 bank on this lesson, from easy to hard. Solve each one, then open "Show answer and explanation". Magmo3 has 63 questions on this lesson, each with an explanation.
According to the book, how many elements form more than 98.5% by weight of the rocks of the Earth's crust?
Correct answer: (D) Eight
Explanation: Although man has identified more than one hundred elements, only eight elements form more than 98.5% by weight of the crust's rocks. Book p.166.
The property that reflects how easily a mineral such as gold, silver or copper can be formed into thinner sheets or wires is:
Correct answer: (B) malleability and ductility
Explanation: Malleability and ductility reflect the ease with which a mineral can be formed into thinner sheets or wires, such as gold, silver or copper. Book p.172.
Sedimentary rocks cover about three quarters of the Earth's crust, but in volume they represent only about:
Correct answer: (D) 5% of the crust's rocks
Explanation: Sedimentary rocks cover three quarters of the crust in relatively thin layers but are only 5% of its rocks by volume; 90% is the share of mudstone, sandstone and limestone among sedimentary rocks. Book p.179.
A crystal has three axes, all unequal in length; two of them are perpendicular and the third is inclined, and it has only one symmetrical plane. Which statement about it is correct?
Correct answer: (A) It is monoclinic, the system to which most minerals belong
Explanation: Three unequal axes with two perpendicular and the third inclined, and only one symmetrical plane, describe the monoclinic system, to which most minerals belong. Book p.168.
Conglomerate and breccia are both cemented gravel rocks with fragments more than two millimetres in diameter. Breccia differs in that:
Correct answer: (D) Its fragments have sharp edges, not rounded ones
Explanation: In the book's clastic table, gravel rocks with rounded fragments are conglomerate and those with sharp edges are breccias; lamination belongs to shale, and volcanic breccia is a separate pyroclastic product around volcanoes. Book p.179.
Pyrite, galena and sphalerite belong to one mineral group. In the book's table of mineral groups, which runs from 'the most' to 'the less', which group comes directly before this group?
Correct answer: (D) Oxides
Explanation: Pyrite, galena and sphalerite are sulphides. The table order is silicates, carbonates, oxides, sulphides, sulphates, then native element minerals, so oxides come directly before sulphides. Book p.166.
In a road cut through layered sedimentary rocks, igneous body X cuts across the bedding planes, while igneous body Y lies parallel to the bedding planes without intersecting them. X and Y are:
Correct answer: (B) X is a dyke and Y is a sill
Explanation: Dykes result when magma is intruded so that it cuts the surrounding rock, and sills when magma is intruded concordant (parallel) with the bedding planes without intersecting them. Book p.178.
A mineral crystal has no symmetrical plane at all. Which description of its axes fits this crystal?
Correct answer: (D) Three axes, all different in length and none perpendicular
Explanation: Only the triclinic system has no symmetrical planes; its three axes are all different in length and are not perpendicular. The monoclinic has one plane, the orthorhombic has vertical and horizontal planes, and the hexagonal has vertical and horizontal planes. Book p.168–169.
In an oil field, oil is found in a sandstone layer although it was generated in a fine-grained muddy layer below. The best explanation is:
Correct answer: (B) The muddy layer is the source rock and oil migrated to the porous reservoir
Explanation: Oil forms from marine micro-organisms buried with fine muddy sediments (source rocks) at 2–4 km and 70–100 °C, then migrates and accumulates in porous reservoir rocks such as sands, sandstone and sometimes limestone. Book p.181.
Mineral X is picked out of a crushed sample with a magnet. Mineral Y belongs to the same mineral group as X and is one of the red ochres that Paleolithic man used to colour his cave walls. Which statement is correct?
Correct answer: (D) Both are oxides, and both are used in steel industries
Explanation: Attraction to a magnet identifies magnetite, and the red ochre of the same group is hematite; both are in the oxides group, and magnetite and hematite are used in steel industries. Book p.165-166, p.172.
The first 10 questions in every subject are free, each with an explanation.