Needed a lot of Google verification in the rocking Geology class today!
Note: Starred clues carry no direct definition,but the seven answers have something in common.
ACROSS
7* Little coverage for the Rhode Island party (10) PERIDOTITE {PE{RI}{DO}TITE}
9 Wish Edward could conceal the outhouse (4) SHED [T]
10* Fancy getting involved in a bet after sacrificing soldiers (8) ANDESITE {AN{DESI
11* Container from the east at the revolutionary ball (6) GABBRO {{GAB<=}{BRO<=}
12 Permission to depart (5) LEAVE [DD]
13 Rogue's bio reviewed by the middle class (9) BOURGEOIS*
14* One framed by an upset editor (7) DIORITE {D{1}ORITE*}
17 Remain with the nun without hesitation after losing 50% of the spice (7) PERSIST
20* Imitate in a clumsy manner after kick-off (9) KOMATIITE {KO}{IMITATE*}
22 Reportedly understood musical direction to remain silent (5) TACET (~tacit) Doubtful homophone
25* Overturned flap covering the Indian tree (6) BASALT {BA{SAL}T<=}
26* Romania retains Henry's margins attached to food low in calories (8) RHYOLITE {R{H
27 Authentic family depiction of the first earl removed by the union leader (4) TRUE TR(-e+u)UE
28 Blunt views on the frigid country? (4,6) COLD TURKEY {COLD} {TURKEY}
DOWN
1 Gathering to bring back and appease ancestors somewhat (6) SEANCE [T]
2 These gates may provide the truth (5) LOGIC [CD]
3 Troubled alien considers alternative brought up for an airplane part (7) AILERON {AILE{RO<=}N*}
4 Rice dish from Korea captures the zest of a couple of Orientals (8) KEDGEREE {K{EDGE}R}{EE} Like our Indian Khitchdi
5 Practical, but powerless, son takes out the knight (6) USABLE U(-n+s)SABLE
6 Narrow escape from the arranged seminars (4,4) NEAR MISS* What happens if it's not a near one? Far miss or Wide escape?
8 Diamonds forgotten in the freeze up (3,4) ICE OVER {ICE} {OVER}
15 Worshipping at sea? Solidarity is missing (8) IDOLATRY
16 Caught Mark after tour with the painted panels (8) TRIPTYCH {TRIP}{TYCH}(~tick)
18 Plaster mould for an office gadget (7) STAPLER*
19 Copper extracted from damaged cutleries is germ-free (7) STERILE
21 Graduate going up with a broken adze gets startled (6) AMAZED {AM<=}{ADZE*}
23 Access the main course (6) ENTREE [DD]
24 Capital sent down to the Japanese city (5) KYOTO (-to)KYO(+to)TO
GRID